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Manipulation of functional properties of the layered materials and their characterization

When atomic periodicity breaks down in electronic materials due to charge defects or some other polarizations, self organized textures forms with ranging scales in space and time, and physical properties of the material suffer large renormalization. The situation is known to occur in different functional materials and in particular in layered systems.


The layered structure topology of functional materials is important due to the fact that electronic degrees of freedom in the layered structures have strongly fluctuating character and the phases with charge (or magnetic order), coexisting with metallic (or superconducting) states can provide an effective mechanism for non-conventional phenomena. On the applied side, layered structures permit to have tuning of properties through external parameters as doping/intercalation, pressure, strain, electric and magnetic fields. This is of key interest for developing new materials through ‘control and manipulation’ for desired properties. Here, the focus is to discuss recent advances in the layered functional materials including emerging superconductors in which inhomogeneous ground state playing important role. In particular quantitative characterization of these materials is a challenging task requiring space and time resolved experimental tools applied under extreme conditions (e.g. pressure, electric and magnetic fields). The symposium welcomes contributions based on theoretical, experimental and applied aspects of the physics, chemistry, materials science on the hot topics given below.

Hot topics to be covered by the symposium:

  • Physics and defect chemistry of layered pnictides and chalcogenides
  • Intrinsic structure of layered and inhomogeneous functional materials
  • Molecular intercalation and functional properties of layered systems
  • Pressure induced phases in layered materials
  • Layered BiS2-based superconductors and thermoelectrics
  • Control and manipulation of different phases and functions in layered systems

List of invited speakers:

  • Tadashi Adachi, SophiaU, Tokyo
  • Yuji Aoki, TMU Tokyo
  • Alexei Barinov, Trieste
  • Sergei Borisenko,Dresden
  • Massimo Capone, Trieste
  • Woo Seok Choi, Suwon
  • Leonardo De Giorgi, ETH Zurich
  • Hong Ding, Beijing
  • Hiroshi Eisaki, Tsukuba
  • Donglai Feng, Shanghai
  • Keun soo Kim, Seoul
  • Yoji Koike, Sendai
  • Kazuhiko Kuroki, Osaka
  • George Martins, Niteroi RJ
  • Kazuyuki Matsubayashi, UEC Tokyo
  • Yoshikazu Mizuguchi, TMU Tokyo
  • Claude Monney, Zurich
  • Minoru Nohara, Okayama
  • Tsutomu Nojima, Sendai
  • Migaku Oda, Sapporo
  • Kenya Ohgushi, Sendai
  • Yukinori Ohta, Chiba
  • Kozo Okazaki, ISSP Tokyo
  • Christos Panagopoulos, Singapore
  • Sidhartha Saxena, Cambridge
  • Shik Shin, ISSP Tokyo
  • Ming Shi, Zurich
  • Thorsten Schmitt, PSI Villigen
  • Young Woo Son, KIAS Seoul
  • Katsumi Tanigaki, Sendai
  • Hide Takagi, Stuttgart
  • Hao Tjeng, MPI Dresden
  • Xingjiang Zhou, Beijin

Tentative list of scientific committee members:

  • Rajeev Ahuja, Uppsala
  • Arun Bansil, Boston
  • Annette Bussmann-Holder, Stuttgart
  • Laszlo Forro, Lausanne
  • Atsushi Fujimori, Tokyo 
  • Takashi Hotta, Tokyo
  • Marina Putti, Genoa
  • Yoshihiko Takano, Tsukuba
  • Takayoshi Yokoya, Okayama
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Transition metal oxides and Mott physics : N.L. Saini
Authors : X.H. LIU, C.F. CHANG, A.D. RATA, A.C. KOMAREK, and L.H. TJENG
Affiliations : Max Planck Institute for Chemical Physics, Dresden, Germany

Resume : Here, we investigate the effect of oxygen stoichiometry, thickness, strain, and microstructure on the Verwey transition in epitaxial Fe3O4 thin films on a variety of substrates. We use MBE technique under UHV conditions combined with in-situ electron diffraction and x-ray spectroscopic characterization as well as ex-situ x-ray diffraction and electrical conductivity measurements. We have been able to determine the factors that affect negatively the Verwey transition in thin films [1], we have investigated in detail the growth mechanism of the interfaces and surfaces which are polar but not-metallic [2] and we have succeeded in growing magnetite films which not only have the Verwey transition as sharp as in the bulk, but also show transition temperatures higher than the bulk [3]. One of the break throughs hereby is that we were able to find a class of substrate materials that is particular for magnetite. Using these tailor-made substrates and the strain exerted by these substrates, our record of the Verwey transition temperature so far, which is the world record as well, is 136.5 K, about 12 K higher than that of the bulk single crystal and about 25 K higher than that of epitaxial thin films so far published. Also, the question of the interplay between the charge and orbital degrees of freedom in magnetite will be discussed. [1] X.H.Liu, et al, Phys Rev B 90, 125142 (2014). [2] C.F.Chang, et al,Phys Rev X 6, 041011 (2016). [3] X.H.Liu, et al, NPJ Quant Mat. 1, 16027 (2016).

Authors : Hiroshi KUMIGASHIRA
Affiliations : Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba 305-0801, Japan

Resume : The extraordinary physical properties of strongly correlated electron systems are usually found in the neighborhood of a quantum phase transition. A typical example is the ubiquitous formation of a superconducting dome surrounding the quantum critical point in the phase diagram of unconventional superconductors. Therefore, the control of quantum criticality is a key strategy to creating these extraordinary physical properties. Here, we report the success in controlling the quantum criticality by the dimensional crossover occurring in metallic quantum well (QW) structures of strongly correlated oxides. With reducing layer thickness to the critical thickness of metal-insulator transition, crossover from a Fermi liquid to a non-Fermi liquid has clearly been observed in the metallic QW of SrVO3 by in situ angle-resolved photoemission spectroscopy. Non-Fermi liquid behavior with the critical exponent α = 1 is found to emerge in the two-dimensional limit of the metallic QW states, indicating that a quantum critical point exists in the neighborhood of the thickness-dependent Mott transition. These results suggest that artificial QW structures provide a unique platform for investigating novel quantum phenomena in strongly correlated oxides in a controllable fashion.

Authors : Katsumi Tanigaki1,2, Yuki Matsuda2, Satoshi Heguri1
Affiliations : 1WPI-Advanced Institute for Materials Research (WPI-AIMR), Tohoku University; 2Department of Physics, Graduate School of Science, Tohoku University, 6-3 Aramaki, Aoba-ku, Sendai 980-8578, Japan

Resume : A similar Mott physics on unconventional superconductors, such as cuprates, heavy fermions, and organic conductors is now claimed for expanded C60 superconductors. However, being different from other unconventional superconductors, electrical transport measurements have been very difficult in C60 fullerides and the discussion has been limited only on a basis of experiments of magnetic probes. Here, we report that accurate electrical transport (ρ) of face-centered-cubic (fcc) fulleride RbxCs3-xC60 (0.35 ≤ x ≤ 3) with expanded lattice volume (V) can successfully be carried out as under various temperature (T) and pressure (P). T/P dependence of electrical resistivity straddling the phase boundary between the Mott insulating and the metallic/superconducting state is carefully studied and compared to the data obtained from magnetic probes. A new phase boundary in the universal T-V(P) phase diagram between the high T Mott phase and the low T metallic phase can be recognized from ρ(T,P), and the result is strikingly contact to the phase boundary determined from magnetic susceptibility (χ(T)). The finding newly viewed from electrical transport indicates that the entropy associated with the freedom of Jahn-Teller lattice deformation plays a crucial role in the universal phase diagram

Authors : Aya Takeda1, Kensei Terashima2, Tetsushi Fukura1, Takanori Wakita2, Takayuki Muro3, Tomohiro Matsushita3, Toyohiko Kinoshita3, Hiromitsu Kato4, Yuji Muraoka2, and Takayoshi Yokoya2
Affiliations : 1The Graduate School of Natural Science and Technology and Research Laboratory for Surface Science, Okayama University, Okayama 700-8530, Japan; 2Research Institute for Interdisciplinary Science(RIIS), Okayama University, Okayama 700-8530, Japan; Japan Synchrotron Radiation Research Institute, Spring-8, Sayo, Hyogo 679-5198, Japan; 4Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST),1-1-1 Umezono, Tsukuba 305-8568, Japan

Resume : Searching superconductivity in materials composed of light elements is one of strategies to discover high transition temperature (Tc) superconductivity. Doped diamond is one such candidate, though the highest Tc so far realized is 10 K in heavily boron-doped diamond[1]. Theoretically, a higher Tc was expected in heavily phosphorus(P)-doped diamond because of higher density of states of the conduction band compared to that of the valence band[2]. P-doped diamond with a P concentration similar to the critical concentration of a metal-insulator transition was made, but doesn’t show metallic behavior. Understanding for the low carrier doping efficiency is important to make P-doped diamond metallic and superconductive. To understand the low carrier doping efficiency, it is essential to know how dopant P atoms in previously observed multiple P chemical sites[3] are incorporated into the lattice. Photoelectron holography is a method capable of observing three dimensional local structure surrounding an atom[4]. In this talk, we present high-resolution photoelectron holography on heavily P-doped diamond and discuss the three dimensional local structures surrounding dopant P atoms in different chemical sites. References: [1] Y. Takano. J. Phys.: Condens. Matter 21, 253201 (2009). [2] Y. Ma et al., Phys. Rev. B 72, 014306 (2005). [3] H.Okazaki et al., Appl. Phys. Lett. 98, 082107 (2011). [4] T. Matsushita et al., J. Electron Spectrosc. Relat. Phenom. 178–179, 195–220 (2010).

10:30 Coffee break    
Excitonic insulators : T. Mizokawa
Authors : H. Takagi1,2,3, Y. F. Lu1, H. Kono1, T. I. Larkin2, A. W. Rost2,3*, T. Takayama2, A. V. Boris2, and B. Keimer2
Affiliations : 1Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan 2Max Planck Institute for Solid State Research, Heisenbergstr. 1, 70569 Stuttgart, Germany 3Institute for Functional Matter and Quantum Technologies, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany

Resume : The excitonic insulator is a long conjectured correlated electron phase of narrow gap semiconductors and semimetals, driven by weakly screened electron-hole interactions. Having been proposed more than 50 years ago, conclusive experimental evidence for its existence remains elusive. Ta2NiSe5 is a narrow gap semiconductor with a small one-electron band gap ΕG of less than 50 meV. Below TC = 326 K a putative excitonic insulator is stabilised. Here we report an optical excitation gap Εop ~0.16 eV below TC comparable to the estimated exciton binding energy EB within the excitonic insulator scenario. Specific heat measurements show the entropy associated with the transition being consistent with a primarily electronic origin. To further explore this physics we map the TC-ΕG phase diagram tuning ΕG via chemical and physical pressure. The dome-like behaviour around ΕG~0 combined with our transport, thermodynamic and optical results are fully consistent with an excitonic insulator phase in Ta2NiSe5.

Authors : Yukinori Ohta
Affiliations : Department of Physics, Chiba University

Resume : The quantum condensation of excitons in thermal equilibrium has attracted renewed attention in recent years. This state, called the excitonic insulator, is an ordered state with spontaneous hybridization between the otherwise unhybridized valence and conduction bands and is described by the pair condensation of fermions, just as in the BCS theory of superconductivity or in the Bose-Einstein condensation (BEC) of preformed pairs. In this talk, starting with a general discussion on the consequences of spin singlet and triplet pair condensations in correlated electron systems, we will focus on one of the candidate materials Ta2NiSe5 for the spin-singlet excitonic insulators. We made the band-structure and model calculations to show that the electronic state near the Fermi level of this material can be described by the three-chain Hubbard model taking into account the lattice degrees of freedom and that the observed phase transition can be explained as the excitonic BEC. Anomalous features in the microscopic quantum interference, as well as those in the specific heat, elastic constant, and diamagnetic susceptibility, were predicted. Moreover, we will give some new perspectives on its excitonic condensation, putting particular emphasis on the strong-coupling nature of excitons, which is evidenced by recent experimental findings, including the optical conductivity, high-pressure effects, and time-resolved photoemission spectroscopy.

Authors : Claude Monney
Affiliations : University of Zurich, Department of Physics, 8057 Zurich, Switzerland

Resume : It has been proposed in 1961 by Mott that a semimetal may be unstable towards an insulating ground state, when electrons and holes bind together through the Coulomb interaction and form excitons [1]. On this basis, it was elaborated a few years later that both a semimetal and a semiconductor can undergo this instability [2]. A phase transition occurs at low temperature, when the excitons condense in a macroscopic state, giving rise to the so-called excitonic insulator phase. Experimental observation of this phase has proven to be very challenging since its theoretical prediction and not much is known about the time-domain dynamics of this exotic phase. In this talk, I will discuss the case of two different materials, which have been proposed as an experimental realization of an excitonic insulator phase. The semimetal TiSe2 has an indirect negative gap (band overlap) and displays a peculiar charge density wave phase transition at 200 K [3]. The semiconductor Ta2NiSe5 has a direct (positive) gap and displays a semiconductor-semiconductor phase transition at about 330 K [4]. In both cases, the free carrier density is very low and the band gap/overlap is small. However, their low energy electronic structures are significantly different. I will present time-resolved angle-resolved photoemission spectroscopy data of both TiSe2 and Ta2NiSe5. I will discuss how these data support a mixed scenario in TiSe2 for which excitonic correlations cooperate with the electron-phonon coupling in triggering the charge density wave phase transition [5]. For Ta2NiSe5, its correlation gap can be increased on the femtosecond timescale in a pump-probe experiment, indicative of a hindered photoinduced phase transition, in contrast to the case of TiSe2 [6]. I will argue that this observation is a direct consequence of the exciton condensate being trapped in a non-thermodynamical state where it is transiently strengthened. References: [1] N. Mott, Phil. Mag. 6, 287 (1961). [2] D. Jérome et al, Phys. Rev. 158, 462 (1967). [3] H. Cercellier et al., Phys. Rev. Lett. 99, 146403 (2007). [4] Y. Wakisaka et al., Phys. Rev. Lett. 103, 026402 (2009). [5] C. Monney et al., Phys. Rev. B 94, 165165 (2016). [6] S. Mor et al., submitted, arXiv:1608.05586.

Authors : Selene Mor 1, Marc Herzog 2, Denis Golež 3, Philipp Werner 3, Martin Eckstein 4, Claude Monney 5 and Julia Stähler 1
Affiliations : 1 Department of Physical Chemistry, Fritz Haber Institute, Berlin, Germany; 2 Department of Physics, University of Potsdam, Potsdam, Germany; 3 Department of Physics, University of Fribourg, Fribourg, Switzerland; 4 Max Planck Research for Structural Dynamics, Hamburg, Germany; 5 Department of Physics, University of Zurich, Zurich, Switzerland

Resume : Ultrafast control of matter phases is of both fundamental and technological interest. Here, we study the ultrafast dynamics of Ta2NiSe5 by means of time- and angle-resolved photoelectron spectroscopy (trARPES) and transient reflectivity measurements. Ta2NiSe5 is proposed to support an excitonic insulator (EI) phase below Tc ≈ 328 K, combined with a structural change from orthorombic to monoclinic symmetry. Such an EI phase is expected to occur in small gap semiconductors with strong electron-hole interaction as excitons can form spontaneously and condense into a ground state. Below Tc, trARPES around k=0 shows a strong fluence-dependent valence band depopulation, until absorption saturates at a critical fluence Fc = 0.2 mJ/cm2. This is reflected in a saturation of the mid-IR optical response at Fc. A coherent phonon at 4 THz, marker of the EI/monoclinic phase, persists above Tc, indicating that the photoinduced structural transition is hindered by pump absorption saturation. trARPES shows that below Fc the band gap shrinks transiently due to photoenhanced screening of the Coulomb interaction, while above Fc it widens and recovers to its equilibrium value after ~1.5 ps. Hartree-Fock calculations reveal that the band gap widening is due to photoenhancement of the exciton condensate, persisting until the system undergoes interband relaxation. Our results prove it is possible to manipulate exciton condensates optically and gain ultrafast control of semiconductor band gaps.

12:30 Lunch break    
Excitonic insulators and functional dichalcogenides : H. Takagi
Authors : Kozo Okazaki
Affiliations : Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan

Resume : Excitonic insulating phase is a spontaneously condensed state of excitons due to their binding energies larger than a band gap. Ta2NiSe5 has been considered as a candidate of excitonic insulators based on its characteristic flat band observed by ARPES measurements [1]. In order to investigate the transient electronic state of Ta2NiSe5, we have performed time- and angle-resolved photoemission spectroscopy using extreme ultraviolet laser from high harmonic generation. The pump fluence dependence of the relaxation dynamics strongly suggests that Ta2NiSe5 is an excitonic insulator. Furthermore, we have observed photo-induced insulator-to-metal transition in Ta2NiSe5. We would like to discuss the mechanism of the observed photo-induced insulator-to-metal transition. [1] Y. Wakisaka, T. Sudayama, K. Takubo, M. Arita, H. Namatame, M. Taniguchi, N. Katayama, M. Nohara and H. Takagi, Phys. Rev. Lett. 103, 026402 (2009).

Authors : K. Matsubayashi(1,2), N. Katayama(3), R. Yamanaka(2), A. Hisada(2), T. Okada(2), A. Nakano(3), H. Sawa(3), K. Munakata(4), A. Nakao(4), T. Kaneko(5), T. Toriyama(5), T. Konishi(6), Y. Ohta(5), Y. Ikemoto(7), T. Moriwaki(7), H. Okamura(8), T. Mizokawa(9), M. Nohara(10), H. Takagi(11,12), Y. Uwatoko(2)
Affiliations : (1) Department of Engineering Science, Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Tokyo, Japan (2) Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, Japan (3) Department of Applied Physics, Nagoya University, Nagoya 464-8603, Japan (4) Comprehensive Research Organization for Science and Society (CROSS), Tokai, Ibaraki, Japan (5) Department of Physics, Chiba University, Chiba, Japan (6) Department of Nanoscience, Chiba University, Chiba, Japan (7) Japan Synchrotron Radiation Research Institute, Sayo, Japan (8) Graduate School of Advanced Technology and Science, Tokushima University, Tokushima, Japan (9) Department of Applied Physics, Waseda University, Shinjuku, Tokyo, Japan (10) Department of Physics, Okayama University, Okayama, Japan (11) Department of Physics, Graduate School of Science, University of Tokyo, Bunkyo-ku, Tokyo, Japan (12) Max Plank Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany

Resume : In narrow gap semiconductors or semimetals with low carrier concentration, it was theoretically predicted that electrons and holes can form bound exciton pairs via weakly screened Coulomb interaction, resulting in a condensation of excitons [1]. Experimental identification of the so-called excitonic insulator (EI) is a long-standing problem in condensed matter physics, however, the investigation of the EI still remains open due to the limited number of known such compounds [2-5]. A promising candidate for the EI is Ta2NiSe5 with a layered structure as verified by recent intensive studies [5-7]. Ta2NiSe5 is a semiconductor with a direct gap and shows a second-order-like structural transition from high temperature orthorhombic to low temperature monoclinic phase at Ts ~ 328 K. A key observation is that below Ts the valence band top becomes extremely flat, suggesting the excitonic instability due to the spontaneous formation of excitons, and this observation is in agreement with theoretical calculations. In this presentation, we report the effect of pressure on Ta2NiSe5 by means of resistivity, ac magnetic susceptibility and x-ray diffraction measurements in order to examine the excitonic scenario via pressure tuning. We found that a semiconductor-semimetal change occurs with increasing pressure while the anomaly at Ts associated with the excitonic insulating state is suppressed to zero temperature at Pc ~ 8 GPa. More interestingly, a superconducting dome emerges with a maximum transition temperature ∼1.2 K in the vicinity of Pc. We will present the pressure-temperature phase diagram of Ta2NiSe5 and discuss the possible interplay of excitonic instability and superconductivity. [1] N. F. Mott, Phil. Mag. 6, 287 (1961). [2] B. Bucher et al., Phys. Rev. Lett. 67, 2717 (1991). [3] H. Cercellier, H. et al. Phys. Rev. Lett. 99, 146403 (2007). [4] A. F. Kusmartseva et al., Phys. Rev. Lett. 103, 236401 (2009). [5] Y. Wakisaka et al., Phys. Rev. Lett. 103, 026402 (2009). [6] Y. F. Lu et al., Nat. Commun. 8, 14408 (2017). [7] K. Seki et al., Phys. Rev. B 90, 155116 (2014).

Authors : Dragan Mihailovic, Yaroslav Gerasimenko, Igor Vaskivsky, Damjan Svetin, Serguei Brazovskii, Petra Sutar.
Affiliations : Jozef Stefan Institute, Ljubljana, Slovenia; CENN Nanocenter, Ljubljana, Slovenia; Univ. Paris Sud, Orsay, France

Resume : The focus in the study of complex systems has recently started to shift from thermodynamic equilibrium states to new emergent non-equilibrium states. This has been stimulated by some recent discoveries of unusual hidden states in a few diverse materials revealed in photoexcitation experiments. The rapid development of new techniques which allow investigations of elementary electronic, spin and lattice structural excitations on short timescales have opened up the possibility of investigating such states in detail. However, the properties of such new emergent states created out of equilibrium are still relatively mysterious, and their relation to equilibrium states is often unclear. The hidden emergent states may be quite delicate, or short lived, and a detailed structure cannot be easily determined. However, if their lifetime is sufficiently long, their intricate structure can be investigated in detail using established high resolution techniques. An excellent example of a material in which the interplay of electronic, spin and lattice degrees of freedom lead to a plethora of equilibrium and non-equilibrium states is the layered quasi-2D tantalum disulphide, whose states are hard to distinguish spectroscopically, but are reveled for the first time with femtosecond-excited scanning tunneling microscopy. Here we present new experimental data on a few such states, including a remarkable new high density amorphous electronic state created under warm dense matter conditions, which is metastable at low temperatures but has a quantum spin liquid ground state. The new discoveries open the way to new functional properties based on topologically protected quantum states in cryogenic memory applications, potentially solving a decades old problem hindering the development of superconducting high performance computing.

Authors : Young-Woo Son
Affiliations : Korea Institute for Advanced Study, Seoul, Korea

Resume : In this talk, I will discuss a couple of novel interplays between structures and electronic properties of layered transition metal dichalcogenides (TMDs). Among several TMDs, three-dimensional MoTe2 and WTe2 share almost similar lattice constants as well as topological electronic properties except their structural phase transitions. While the former shows a well-known first order phase transition between monoclinic and orthorhombic structures, the latter does not. Using a state-of-the-art first-principles calculation method, we investigate their structural stability and uncover that the disparate phase transitions originate from delicate differences between their interlayer bonding states near the Fermi energy. By exploiting the relation between the structural phase transitions and the low energy topological electronic properties, we show that a charge doping can control the transition substantially, thereby suggesting a way to stabilize or to eliminate their topological electronic energy bands. I will also discuss the electronic phase diagram of the both materials as a function of external charge doping. I show that in low doping, enhanced electron-phonon interactions enhance the superconducting (SC) transition temperatures. As increasing doping density, the SC temperature gradually decreases to zero and then various new CDW states emerge. Physical origins of new collective phenomena will be briefly discussed.

15:30 Coffee break    
Iron based layered superconductors-I : K. Kuroki
Authors : Minoru Nohara
Affiliations : Okayama University

Resume : The effects of chemical doping on the structural and superconducting phase transitions of BaNi2As2 were studied. We found an abrupt increase in the superconducting transition temperature Tc from 0.6 K in the triclinic phase with less doping to 2.5–3.3 K in the tetragonal phase with more doping at x = 0.067 for BaNi2(As1−xPx)2 [1] and at x = 0.16 for Ba(Ni1−xCux)2As2 [2]. Specific-heat data suggested that doping-induced phonon softening was responsible for the enhanced superconductivity in the tetragonal phase [1, 2]. [1] K. Kudo, M. Takasuga, Y. Okamoto, Z. Hiroi and M. Nohara, Phys. Rev. Lett. 109 097002 (2012). [2] K. Kudo, M. Takasuga and M. Nohara, arXiv:1704.04854.

Authors : M. Chinotti 1, A. Pal 1, L. Degiorgi 1, A.E. Böhmer 2, P.C. Canfield 2
Affiliations : 1 Laboratorium für Festkörperphysik, ETH - Zürich, CH-8093 Zürich, Switzerland 2 Ames Laboratory, Ames, Iowa 50010, U.S.A.

Resume : FeSe undergoes a structural tetragonal-to-orthorhombic transition below 90 K, which breaks the four-fold rotational symmetry of the tetragonal phase, without any subsequent onset of magnetic ordering. FeSe thus provides an opportunity to address the impact of nematicity on its intrinsic physical properties without the limitations of the reconstruction of the Fermi surface due to the SDW collective state in the orthorhombic phase, typical for several other iron-based superconductors. We describe results of reflectivity measurements over a broad spectral range that probe the optical response to variable uniaxial stress, detwinning the specimen and acting as an external symmetry breaking field, and as a function of temperature across the structural transition. We extract the optical conductivity through Kramers-Kronig transformation. Our findings reveal an astonishing anisotropy of the optical response in the mid-infrared-to-visible spectral range, which bears testimony of an important polarization of the underlying electronic structure in agreement with ARPES results. Our findings support models for the nematic phase based on an orbital-ordering mechanism, supplemented by orbital selective band renormalization. The far-infrared response of the charge dynamics moreover allows establishing the link to the dc resistivity. The dc limit of the optical conductivity indeed agrees with the measured transport properties, deploying an anisotropy typical of hole-doped iron-based materials. In our presentation, we will also emphasize the comparison between our newest results on FeSe and our early data on the representative Co-underdoped 122-iron-arsenides.

Authors : Y. Koike, T. Hatakeda, S. Hosono, K. Sato, S. Nakamura, T. Noji, T. Kawamata, M. Kato
Affiliations : Department of Applied Physics, Tohoku University, Sendai 980-8579, Japan

Resume : Our recent works on the superconductivity in alkali-metal- and organic-molecule-intercalated transition-metal chalcogenides are reviewed. We have succeeded in the synthesis of new superconductors of ethylenediamine-intercalated Ax(C2H8N2)yFe2-zSe2 (A = Li, Na) [1,2], hexamethylenediamine-intercalated Lix(C6H16N2)yFe2-zSe2 [3-5] and 2-phenethylamine-interclated Ax(C8H11N2)Fe1-zSe (A = Li, Na) [6] with Tc = 38 – 45 K. In the FeSe-based intercalation superconductors, Tc is saturated at ~ 45 K for the interlayer spacing between FeSe layers d > 9Å. This saturated value of Tc is comparable to Tc values of single-layer FeSe films. Accordingly, the electronic structure of the single-layer FeSe films has been concluded to be similar to that of the FeSe-based intercalation superconductors with large d values. We have also succeeded in the synthesis of new superconductors of Lix(C2H8N2)yMSe2 and Lix(C6H16N2)yMSe2 (M = Ti, Mo) with Tc = 2.4 - 6.0 K. As for M = Ti, the electron doping by Li and the expansion of the interlayer spacing by diamines have been found to suppress the CDW transition in TiSe2, leading to the appearance of superconductivity. As for M = Mo, Tc has been found to be related not to the interlayer spacing but to the carrier density increased by Li. We have also succeeded in the synthesis of a new superconductor of (C2H8N2)yTa2PdSe6 with Tc = 4.5 K. The electronic polarization of ethylenediamine may play a role in the appearance of superconductivity. [1] T. Hatakeda et al., J. Phys. Soc. Jpn. (JPSJ) 82, 123705 (2013). [2] T. Noji et al., Physica C 504, 8 (2014). [3] S. Hosono et al., JPSJ 83, 113704 (2014). [4] S. Hosono et al., JPSJ 85, 013702 (2016). [5] S. Hosono et al., JPSJ 85, 104701 (2016). [6] T. Hatakeda et al., JPSJ 85, 103702 (2016).

Authors : Hong Ding
Affiliations : Institute of Physics, Chinese Academy of Sciences, Beijing

Resume : In this talk I will report our recent results on searching for topological superconductivity in Fe-based su-perconductors. We have obtained clear and strong ARPES evidence of 2D topological superconductivity on the surface of Fe(Te,Se) single crystals with Tc ~ 15K. We will demonstrate that there is a Majorana bound state in the vortex core on this superconducting topological surface. Furthermore, Our ARPES re-sults on Fe(Te,Se)/STO monolayer indicate that the 1D edge state of this monolayer materials may be-come high-temperature topological superconductor at a certain Te concentration. This intrinsic topologi-cal Fe(Te,Se) superconductor, which takes advantage of the natural surface/edge and interband supercon-ducting coherence in the momentum space, may pave a new and exciting route for realizing topological superconductivity and Majorana fermions under higher temperature.

Poster session : T. Mizokawa, T. Yokoya, C. Kim
Authors : D. D. Damm1, A. Contin2, A. E. N. Andrade3, V. J. Trava-Airoldi2, D. M. Barquete4, E. J. Corat2.
Affiliations : 1São Paulo Federal University, São José dos Campos, São Paulo, Brazil; 2National Institute for Space Research, São José dos Campos, São Paulo, Brazil; 3 ETEP Faculty of Technolog , São José dos Campos, São Paulo, Brazil; 4 Santa Cruz State University , Ilhéus, Bahia, Brazil

Resume : Several types of interfaces have been developed to make possible the deposition of CVD diamond on steels. Among these materials, vanadium carbide (VC) is a promising material due its following characteristics: high adherence to the carbon steel substrate, hardness of 3200-3800 HV, forms a low-porous film and has intermediate CTE (6.06x10-6K-1) between steel (11.6x10-6K-1) and diamond (0.8x10-6K-1). The intermediate coating should have the ability to attenuate the thermal stresses caused by cooling and to provide an efficient diffusional barrier preventing the transition metals migration to the reaction region on the sample surface avoiding the formation of graphite. The graphite presence reduces adhesion and the quality of the diamond film. The objective of this work is the improvement of vanadium carbide films for the deposition of HFCVD diamond in the development of high performance cutting tools. The conditions of the thermo reactive process were systematic changed to promote greater suitability of the VC coating to the deposition of the CVD diamond. The diamond films deposition occurred in a HFCVD reactor for a 3h period. The results were obtained by X-ray diffraction, scanning electron microscope, Rockwell C test and Raman spectroscopy.

Authors : A. Vlad1, I. Tirca1,2, M. Secu3, R. Birjega1, R. Zavoianu4, A. Matei1, A. Marinescu1, M. Dinescu1
Affiliations : 1 National Institute for Lasers, Plasma and Radiation Physics,Atomistilor 409, Bucharest, Romania, 2University of Craiova, Faculty of Sciences, RO-200585, Craiova, Romania 3National Institute for Materials Physics, P.O. Box MG-7, 77125 Bucharest-Magurele, Romania 4 University of Bucharest, Faculty of Chemistry, Department of Chemical Technology and Catalysis, 4-12 Regina Elisabeta Bd., Bucharest, 030018, Romania

Resume : Preparation of functional thin films of Mg-Al layered double hydroxide (LDH) with Mg/Al molar ratio of 2.5, organic coumarin intercalated Mg-Al LDH thin films and coumarin and dodecyl sulfate (DS) surfactant co-intercalated MgAl-LDH thin films have been investigated. Pulsed laser deposition (PLD) technique using a Nd:YAG laser (266, 532 and 1064 nm) working at a repetition rate of 10 Hz have been employed. The co-precipitation at constant pH under high supersaturation conditions was the method employed for the synthesis of the Mg-Al layered double hydroxide (LDH) powders with and without organic coumarin and dodecyl sulfate surfactant intercalated or co-intercalated. Gracing incidence - X-Ray Diffraction (GI-XRD) and photoluminescence measurements performed on the obtained thin films show that these organic-inorganic functional thin films obtained via pulsed laser deposition (PLD) have prospective application as photoluminescence materials.

Authors : Xiaoyu Jia, X. Chen, Y. J. Yu, T. P. Ying, X. L. Chen, S. Y. Li
Affiliations : State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China; Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100190, China; Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China; University of Chinese Academy of Sciences, Beijing, 100049; Collaborative Innovation Center of Quantum Matter, Beijing, China.

Resume : After chemical doping of AuTe6, a layered superconductor has been grown. The structure is mostly like a unique 2D compound that is realized by anisotropic stacking of cubes with diverse Te-Te covalent bonds. The ultra-low-temperature thermal conductivity measurement is a powerful bulk technique to probe the superconducting gap structure. Here we performed low-temperature thermal conductivity measurements down to 100mK on this new 2D superconductor and revealed the gap structure.

Authors : Sajid-ur-Rehman, Faheem K. Butt, Chuanbo Li, Bakhtiar Ul Haq
Affiliations : a State Key Laboratry on Integrated Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, 100083, Beijing, China b Department of Physics, The University of Lahore, 1-Km Raiwind Road, Lahore, 53700, Pakistan. cAdvanced Functional Materials & Optoelectronics Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha, Saudi Arabia.

Resume : First principles calculations are carried out for calculating the electronic structure and optical properties of nitrogen doped Sb2Se3. DFT based calculations were performed on bulk Sb2Se3 and N-doped Sb2Se3 (on Sb and Se sites) system with 1 and 2 atoms. The electronic band structure indicates that when 1 and 2 N atoms were introduced into Sb sites the bandgap of Sb2Se3 is significantly reduced from 1.11 eV to 0.787 and 0.685 eV respectively. Contrary, when N atom is introduced to Se site, it shows a metallic behavior. The calculated values of static dielectric function ?1(0) are 14.84, 15.54, 15.02, 18.9 and 39.29 for Sb16Se24, Sb15N1Se24, Sb14N2Se24, Sb16Se23N1 and Sb16Se22N2 respectively. The static refractive index n(0) for Sb16Se24, Sb15N1Se24, Sb14N2Se24, Sb16Se23N1 and Sb16Se22N2 are 3.83, 3.92, 3.86, 4.33 and 6.21 respectively. In N doping at Sb sites exhibits a substantial red shift towards the short-wave infrared light region compared to Se sites in optical absorbance and optical conductivity. Modulation of the static dielectric constant and static refractive index is primarily dependent on N doping. The bandgap narrowing effect and Optical properties signify that the N-doped Sb2Se3 is a favorable new semiconductor material for Solar Cells and Infrared Optoelectronic Devices.

Authors : A.E. Hafarov, I.A. Vladymyrskyi, S.I. Sidorenko
Affiliations : National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Kyiv, Ukraine

Resume : Due to the strong magneto-crystalline anisotropy nanoscaled heterolayers based on ordered L10-FePt phase are promising material for applications in ultra-high density magnetic storage. It is known that almost full intermixing of components in thin film heterostructures can occur through grain boundary diffusion and grain boundary diffusion induced motion at low temperatures when bulk diffusion processes are practically absent. At the same time, the enhancing of L10 ordering can be achieved by the introduction of third elements such as Ag, Au, or Cu. In this study, the effect of an intermediate Au layer on the evolution of the low-temperature FePt phase formation in Pt/Au/Fe thin films was investigated. According to XRD analysis and SNMS investigation an enhancement of the low-temperature intermixing of nanocrystalline Fe and Pt thin films caused by the introduction of an additional intermediate Au layer. The grain boundary diffusion induced reaction layer formation mechanism is the main mechanism which causes an intermixing at relatively low temperatures. Furthermore, the ordering is also enhanced, leading to the appearance of the chemically ordered L10-FePt phase, which results in a strongly increased coercivity. The enhanced chemical L10 ordering is explained by the development of stresses during disordered A1 FePt formation along the grain boundaries.

Authors : T. Ouchi, S. Tanaka, Y. Iwasa, and T. Nojima
Affiliations : Institute for Materials Research, Tohoku University; QPEC and Department of Applied Physics, The University of Tokyo; RIKEN Center for Emergent Matter Science

Resume : The spin-momentum locking caused by Rashba-type spin-orbit interaction (SOI) is one of the attractive phenomena in gated two-dimensional electron system, since it can induce the spin-polarized state without magnetic order. Especially, for the electron doped (001) surface of SrTiO_3 with broken inversion symmetry, the characteristic spin texture with the spin polarized vectors limited only to the [100] or [010] direction has been predicted theoretically as a consequence of the enhancement of Rashba SOI in combination with the multi-orbital effect of Ti-3d electrons. However, this special spin state has not been proved experimentally. In this presentation, we demonstrate the magnetotransport of ion-gated SrTiO_3 (001) surfaces with the electric double layer transistor configuration detects the spin polarized state induced by the enhanced Rashba SOI. We prepared the conducting surface with carrier density ranging from 0.3 to 4.2×10^14 cm^-2. For all the samples, the negative magnetoresistance MR is observed in the in-plane magnetic fields, implying the spin polarization. We found the oscillating behavior of MR with 2-fold symmetry component (low carrier density) or 4-fold component showing minimums at the [100] and [010] direction (high carrier density) against the in-plane rotation of magnetic field, accompanied with the planer Hall effect. These results indicate the development of spin polarized state from isotropic to anisotropic helical one depending on carrier density, as predicted theoretically. We discuss the combined phenomena of anisotropic MR and planer Hall effect, which are usually observed in ferromagnetic films, originates only from the spin-momentum locking in our non-magnetic system.

Authors : Irene Cascallana-Matías, Jessica C. McGlynn, Alexey Y. Ganin
Affiliations : School of Chemistry, WestCHEM, University of Glasgow, Glasgow, United Kingdom

Resume : Since their discovery over a decade ago layered iron-based chalcogenides (IBCs) have become a prominent class of high temperature superconductors. One of these IBCs is binary FeSe, which has a tetragonal structure consisting of layers built upon edge-sharing FeSe4 tetrahedra. The weak interactions between the layers has enabled rich intercalation chemistry into FeSe. Small cationic species and even small molecules can occupy the interlayer space making FeSe, despite a moderately low Tc = 8.5 K, an important archetypal compound for new IBCs superconductors. However, the intercalation process is often carried out at elevated temperatures via solid state routes or using a soft chemistry approach. Despite apparent successes, the typical chemical approach allows only the formation of the thermodynamically stable phases due to limited control over the intercalation process. Furthermore, due to low oxidation state of Fe2+ within FeSe overreduction processes, by “leeching” of metal Fe, are often competing with the formation of the metastable (and potentially superconducting) products. In this work we demonstrate that Na intercalation into FeSe can be efficiently governed via electrochemical intercalation reaction, confirmed by XRD studies. Precise control is achieved over the content of inserted Na solely by tuning the current and the charge time. SQUID measurements show that the newly formed compound is a superconductor with a Tc = 45 K – a quintuple improvement over the pristine FeSe precursor phase.

Authors : Yanyong Li, Zhixin Hu, Shenghuang Lin, Sin Ki Lai, Wei Ji, Shu Ping Lau
Affiliations : Yanyong Li, Shenghuang Lin, Sin Ki Lai, Shu Ping Lau; Department of Applied Physics, The Hong Kong Polytechnic University; Zhixin Hu, Wei Ji; Department of Physics and Beijing Key Laboratory of Optoelectronic Functional Materials and Micro-Nano Devices, Renmin University of China

Resume : Since graphene was discovered in 2004, various two-dimensional layered materials, such as molybdenum disulfide, hexagonal boron nitride and gallium selenide, attract lots of attention due to the fantastic properties compared to their bulk counterparts.[1-3] Both advantages and drawbacks are discovered in those 2D materials, which stimulates people to explore novel 2D layered materials with both the intrinsic finite band gap and high carrier mobility. Black phosphorus (BP), the most stable allotrope of phosphorus, is regarded as the most promising candidate for complementing graphene’s deficiencies. BP has a thickness-dependent band gap varying from 0.3 eV to 2.0 eV just bridging the gap between graphene and the family of transition metal dichalcogenides.[4] Remarkably, unlike the perfectly flat layer in graphene, the puckered hexagonal structure of BP results in apparent zigzag and armchair edges, which leads to lots of intriguing features. For example, the electrical conductance along the armchair (AC) direction is about 1.5 times larger than that along the zigzag (ZZ) direction.[5] On the other hand, ZZ direction is a preferential thermal conduction path.[6] It is predicated that the colossal anisotropy in BP can be modified by strain engineering.[7] And theoretical calculations show that monolayer BP can even sustain a remarkable tensile strain of 30%.[8] Together with the different ZZ and AC direction, black phosphorus could pave the way for creating novel strain tunable devices. So, it is valuable the investigate the anisotropy in few-layer BP. However, there is still lack of experimental demonstration of the anisotropic strain response due to the instability of few-layer BP in ambient environment.[9] Herein, we comprehensively investigated the colossal Raman anisotropy of few-layer BP to the applied uniaxial strain. The few-layer BP was encapsulated by a layer of polymethyl methacrylate (PMMA) to avoid the degradation and enhance the strain transfer efficiency. It is found that the Raman shift rates of the three characteristic Raman modes, A_g^1, B_2g and A_g^2, are significantly distinct for the uniaxial strain applied along different directions. When the strain is applied along the ZZ direction, the Raman shift rate of the B_2g mode reaches a remarkable value of ~ -11 cm-1/% strain. And the Grüneisen parameter is as high as ~ 2.5, which is the largest among all the reported common 2D layered materials. However, the outcomes are dramatically different, when the uniaxial strain is applied along AC direction. The Raman shift rate of the B_2g mode declines to ~ -1.85 cm-1/% strain. Density functional perturbation theory calculations were performed to understand the origin of the colossal anisotropic strain response discovering that not only the bond lengths but also the bond angels were changed in the strained few-layer BP. Furthermore, we demonstrate an alternative method based entirely on the strained few-layer BP and non-polarized Raman spectroscopy to determine the crystallographic orientations of few-layer BP, which only depends on the variations of Raman shift. Our work paves a way to study the strain-induced anisotropic electrical conductance and magneto-transport properties of few-layer BP. References [1] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science 2004, 306, 666. [2] A. Splendiani, L. Sun, Y. Zhang, T. Li, J. Kim, C. Y. Chim, G. Galli, F. Wang, Nano Lett. 2010, 10, 1271. [3] A. Loiseau, F. Willaime, N. Demoncy, G. Hug, H. Pascard, Phys. Rev. Lett. 1996, 76, 4737. [4] H. O. Churchill, P. Jarillo Herrero, Nat. Nanotechnol. 2014, 9, 330. [5] F. Xia, H. Wang, Y. Jia, Nat. Commun. 2014, 5, 4458. [6] Z. Luo, J. Maassen, Y. Deng, Y. Du, R. P. Garrelts, M. S. Lundstrom, P. D. Ye, X. Xu, Nat. Commun. 2015, 6, 8572. [7] R. Fei, L. Yang, Nano Lett. 2014, 14, 2884. [8] X. Peng, Q. Wei, A. Copple, Phys. Rev. B 2014, 90, 085402. [9] A. Castellanos-Gomez, L. Vicarelli, E. Prada, J. O. Island, K. L. Narasimha-Acharya, S. I. Blanter, D. J. Groenendijk, M. Buscema, G. A. Steele, J. V. Alvarez, H. W. Zandbergen, J. J. Palacios, H. S. J. van der Zant, 2D Mater. 2014, 1, 025001.

Authors : Dong-Won Shin (1), Seong Il Cho (1), Hye Kyeong Sung (1), Young-Jin Kim (1), Sang-Won Gwak (2), Soo Chang Lee (3), Yoon Soo Han (1)
Affiliations : (1) Catholic University of Daegu; (2) Korea E&S Co., Ltd.; (3) Interojo Inc.

Resume : Silicone hydrogel (SH) contact lenses have shown marked improvement over conventional hydrogel lenses by allowing extended periods of wear time without inducing corneal hypoxia. General SH lenses are siloxane-based polymers, rather than water, for oxygen transport through the bulk of the lens. However, theses SH contact lenses suffer from low water content - it could result in dry eye symptoms such as irritated, scratchy and red eyes when wearing them. Thus, it is necessary to incorporate hydrophilic coating on the surface of SH contact lens. Water soluble cellulose is already familiar in industry where it is used as a viscosity modifier or thickener, and to stabilize emulsions in various products. It is also nontoxic and biodegradable. In this study, we investigated crosslinking behavior of water soluble cellulose using various crosslinkers and a possibility of the crosslinked cellulose as a surface coating layer with high water content on SH contact lenses. The principal results of the work are: (1) Cross-linked cellulose films were successfully prepared by reaction of water soluble cellulose and a crosslinker, (2) Water content of the cross-linked cellulose films was measured by 75%, and it was decreased with increasing the crosslinker in the reaction solution, and (3) By adjusting the reaction condition, we could control the thickness of the cross-linked cellulose film on the silicon hydrogel lens, ranged from 400 to 2,000 nm.

Authors : Hyunsub Kim, Song-Ho Byeon
Affiliations : Department of Applied Chemistry, College of Applied Science, Kyung Hee University, Korea

Resume : Copper plays a crucial role in human metabolic processes. Human body needs copper for a number of reasons such as keeping our immune system healthy and forming red blood cells. However, our daily diet requires only trace amounts of copper. In fact, the World Health Organization (WHO) set the limit of Cu content in drinking water to 31.5μM because excessive amounts of copper may lead to serious health problems, often with fatal consequences. Hence, the development of an accurate but simple method for copper detection and elimination would be significantly beneficial in improving human lives. As we previously reported, YVO4:Eu nanoparticles have high affinity towards copper so as to be utilized to reach this goal. In this study, Eu-doped layered yttrium hydroxide (LYH:Eu) films were deposited on the glass substrates using a chemical bath deposition (CBD) technique. YVO4:Eu nanoparticles could be then tailored at the edge of LYH nanosheets by reacting these films in aqueous NaVO3 solutions. The negative surface potential of films, which is caused by a lot of remnant surface hydroxyl groups of tailored YVO4:Eu nanoparticles, resulted in the intensive adsorption of Cu2+ ions thru electrostatic attraction. Although as-prepared Eu-doped YVO4/LYH film showed strong red emission under UV irradiation, the adsorption reaction of Cu2+ ions at the film surface in aqueous solution dramatically weakened its emission intensity. This luminescence quenching is associated with the effective filter effect resulting from the complimentary overlapping of the emission band of YVO4:Eu with the absorption band of Cu2+ ions. Our films could be employed for the development of sensitive copper detection and/or removal technology under various conditions.

Authors : Weiping Gong1, Zhaohui Guo1, Weidong Xie1, Min Liu1, S. Sidorenko2, S. Zamulko2, M. Fedorov2, S. Voloshko2, G. Kholmska2
Affiliations : 1 Laboratory of Electronic Functional Materials, Huizhou University, PRC; 2 Metal Physics Department, Igor Sikorsky Kyiv Polytechnic Institute, Ukraine

Resume : One of the main problems of solar cells with Si working area and Ag front contact grid is contact degradation, because Ag has high diffusivity, which is also enhanced by the electric current. Through time, electrical resistivity of such contact interface grows, resulting in low conversion efficiency. New generation contacts include coating of silver grid with diffusion barrier material (Me) and covering the surface with Graphene monolayer (G) to overcome presumable lowering of contact conductivity. In order to design contacts of new generation it is necessary to investigate the properties of Ag/Me, and Me/G interfaces. In previous works the diffusion properties of coating were investigated in order to find the diffusion barrier for Ag. The aim of the current work was to investigate the electrical resistivity of Ag/Me interface. Simulations were conducted in Abinit software using the LDA Troullier-Martins pseudopotentials and PAW pseudopotentials. FCC lattice structure was chosen for all materials despite their stable lattice, representing the epitaxial growth of coating on the Ag conductive grid. Other important properties of materials were analyzed in literature and combination of best properties gave the preferable material for application in the solar cell contacts coating.

Authors : K. Golasa (1) , L. Bala (1), M. R. Molas (2), K. Nogajewski (2), M. Bartos (2) , M. Potemski (1)(2), A. Babinski (1)
Affiliations : (1) Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland (2) LNCMI, CNRS-UGA- UPS-INSA- EMFL, 25 rue des Martyrs, 38042 Grenoble, France

Resume : One of the most spectacular features of semiconducting transition metal dichalcogenides (S-TMDs) is the fact that band gap in these materials changes from indirect to direct when decreasing number of layers, which makes photoluminescence (PL) in monolayer much stronger than in bulk. In spite of this, it is still possible to enhance PL further by the use of TFSI (bis(trifluoromethane) sulfonamide) superacid, which increases recombination efficiency from below 2 to even 90 percent and quenches the defect-related PL, making exciton recombination a dominant process. We present results of (PL), reflectance and Raman scattering study of superacid treated MoS2 monolayer. Samples were obtained by means of a standard exfoliation technique of bulk and then deposited on Si/SiO2. After initial characterization a certain number of MoS2 layers were passivated in superacid. A significant reduction of the low energy emission, ascribed to the defect-related excitons was noticed progressing with each successive passivation process. Moreover, contrary to previous reports, we found a substantial redshift of the free exciton (X) energy. Two features, tentatively ascribed to the intravalley (T1) and intervalley (T2) trions of the same charge, were clearly apparent in the as-exfoliated MoS2. They were annihilated from the PL spectrum as a consequence of passivation processes, leaving dominant emission due to the neutral exciton (X). We observe several changes in resonant (1.96eV) Raman scattering spectra. The most prominent one is the enhancement of characteristic Raman features, including A'1 and E'2 peaks. Furthermore, new structures arise, which haven't been reported previously.

Authors : Alessandra Leonhardt, Daniele Chiappe, Inge Asselberghs, Nicolo Pinna, Ashish Dabral, Ankit Nalin Mehta, Thierry Conard, Johan Meersschaut, Cedric Huyghebaert, Iuliana Radu, Stefan de Gendt
Affiliations : imec and Department of Chemistry / KU Leuven; imec; imec; imec; imec and Department of Physics and Astronomy / KU Leuven; imec and Department of Physics and Astronomy / KU Leuven; imec; imec; imec; imec; imec and Department of Chemistry / KU Leuven

Resume : 2D transition metal dichalcogenides (TMDC) are versatile materials for beyond-silicon CMOS scaling. Due to their discrete number of layers, they provide improved electrostatics for short channel applications. The Van der Waals interlayer interactions allow very flexible integration schemes for these 2D TMDC?s, such as heterogeneous co-integration with silicon logic devices. But while 2D TMDC are suited for various applications, drawbacks such as high contact resistance and low experimental mobility hinder their development [1]. Material performance can be affected by processing steps and environmental exposure. Here we assess the impact of processing and exposure to oxidants on electrical parameters such as contact resistance and mobility. Although MoS2 is not considered unstable in air, as other 2D semiconductors such as silicene [2] and phosphorene [3], it is still prone to oxidation. Sulfur vacancies, which are commonly considered to be the source of the n-type conduction in MoS2 [4] are readily passivated by oxidants, when exposed [5]. The impact of sulfur vacancies and their oxidation is discussed, with defect engineering being explored as a possible way to tailor MoS2 electrical parameters. This work highlights the issues of partial instability in wafer scale MOCVD MoS2 [6] and proposes a procedure to avoid layer oxidation, which reduces the contact resistance of back-gated transistors by almost two orders of magnitude. We discuss the effects of oxidants both in the channel regions and contact regions of MoS2 transistors through a systematic study. We show that by avoiding ambient exposure, we can reduce contact resistance by two orders of magnitude (if the contact region is protected) and increase mobility by 50% (if the channel region is protected). [1] Duan, X., Wang, C., Pan, A., Yu, R. & Duan, X. Two-dimensional transition metal dichalcogenides as atomically thin semiconductors: opportunities and challenges. Chem. Soc. Rev. 44, 8859?8876 (2015). [2] Molle, A. et al. Hindering the Oxidation of Silicene with Non-Reactive Encapsulation. Adv. Funct. Mater. 23, 4340?4344 (2013). [3] Island, J. O., Steele, G. A., Zant, H. S. J. van der & Castellanos-Gomez, A. Environmental instability of few-layer black phosphorus. 2D Mater. 2, 11002 (2015). [4] Kim, I. S. et al. Influence of Stoichiometry on the Optical and Electrical Properties of Chemical Vapor Deposition Derived MoS2. ACS Nano 8, 10551?10558 (2014). [5] Kc, S. et al. Surface oxidation energetics and kinetics on MoS2 monolayer Surface oxidation energetics and kinetics on MoS 2 monolayer. J. Appl. Phys. 117, 135301 (2015). [6] Kang, K. et al. High-mobility three-atom-thick semiconducting films with wafer-scale homogeneity. Nature 520, 656?660 (2015).

Authors : Amjid Rafiquea*, Mara Serrapede , Paola Rivolo, Marco Fontanaa,b, , Stefano Biancoa,b, Usman Zubair, Bordoardo Silvia ,Candido F. Pirria,b and Andrea Lambertia,b
Affiliations : • a Politecnico di Torino, Dipartimento di Scienza Applicata e Tecnologia (DISAT), Corso Duca Degli Abruzzi, 24, 10129 Turin, Italy. • b Istituto Italiano di Tecnologia, Center for Sustainable Future Technologies, Corso Trento, 21, 10129 Turin, Italy

Resume : In recent past, transitional metal dichalcogenides attained great interest of researchers due to their potentialities as electrochemical active compounds. Two-dimensional molybdenum disulphide MoS2 nanoplates are low-cost and environmental friendly materials for energy storage devices and energy conversion. We demonstrated the possibility to synthesize by a green hydrothermal process in autoclave the mixed phase of 1T-2H phase of MoS2 onto reduced graphene oxide [1] showing outstanding performances as electrode for supercapacitors in aqueous electrolyte. Herein, we compare the electrochemical behaviour of MoS2 decorated carbon fibers fabricated by different methods such as electrophoretic deposition [2], electrochemical deposition [3] and direct drop-casting of MoS2 onto the CFs. The unique physical and chemical properties of the MoS2-CFs will be shown together with their performances towards hydrogen evolution reaction HER at different coverages (1 mA cm-1 at -0.2 V vs. NHE for 250 g cm-1 at 0 pH) and capacitance at different pHs (30 mF cm-1 at 20 mV s-1 at 0 pH). Moreover, promising results obtained for binder-free flexible supercapacitor devices will be shown. [1] DOI:10.1021/acsami.6b11290 ACS Appl. Mater. Interfaces 2016, 8, 32842−32852 [2] Scientific Reports 6, Article number: 22516 (2016) doi:10.1038/srep22516 [3] Materials Science in Semiconductor Processing 32:31-39 · April 2015 DOI: 10.1016/j.mssp.2015.01.006

Authors : G.A. Nemnes (1,2), T.L. Mitran (2), A. Manolescu (3), Daniela Dragoman (1)
Affiliations : (1) University of Bucharest, Faculty of Physics, MDEO Research Center, 077125 Magurele-Ilfov, Romania; (2) Horia Hulubei National Institute for Physics and Nuclear Engineering, 077126, Magurele-Ilfov, Romania; (3) School of Science and Engineering, Reykjavik University, Menntavegur 1, IS-101 Reykjavik, Iceland

Resume : Unlike in graphene monolayer, in the AB-stacked bilayer graphene (BG) one can induce a non-zero bandgap by breaking the inversion symmetry of the two layers using a perpendicular electric field [1], which is essential in field-effect applications. Moreover, the gap may be tuned by the magnitude of the external electric field. Doping is another way to modify the electronic properties of BG systems. Experimentally, nitrogen doped BG has been achieved by hyperthermal ion implantation [2]. Theoretical ab initio investigations confirm the p-type and n-type electronic properties of BG doped with boron and nitrogen [3]. We investigate here doped BG systems in the presence of an external electric field, in the framework of density functional theory (DFT) calculations, employing van der Waals functionals. Highly doped boron/nitrogen BG systems behave as degenerate p/n semiconductors, where the Fermi energy depends on the doping concentration but also on the applied electric field. Increasing the electric field, the gaps become larger and shift toward the Fermi level, decreasing the effect of extrinsic doping. In this context, we discuss the possibility of using external electric fields to suitably adjust the effective doping in BG systems. References: [1] Yuanbo Zhang et al., Nature 459, 820 (2009); [2] C. D. Cress et al., ACS Nano 10, 3714 (2016); [3] Y. Fujimoto et al., Surf. Sci. 634, 57 (2015).

Authors : Min-seon Lee(a,b), Youn-woo Hong(a), Jeong-ho Cho(a), Jong-hoo Paik(a), Yong Ho Park(b), Young Hun Jeong(a, *)
Affiliations : a Electronic Convergence Materials Division, Korea Institute of Ceramic Engineering and Technology, South Korea b Department of Material Science and Engineering, Pusan National University, South Korea

Resume : The structure and acoustic properties of lead zirconate titanate (PZT) multi-layered piezoelectric actuators were evaluated for directional speaker applications. The PZT ceramic sheets formed by a tape casting process were laminated to be approximately 400 nm-thick under high pressure of 3000 psi. Co-firing at 1050oC was conducted on the PZT multi-layers, and thereafter, the sintered specimen was successfully poled along the thickness axis in order to drive the transversal vibration mode. It exhibited a highly dense microstructure and a flat shape after co-firing process. The Ag-Pd interdigitated metal electrode (IME) patterns with width (IME finger) and gap (adjacent IME fingers) of 100 ?m and 500 ?m, respectively, were also fabricated on a polyimide substrate for vibrating diaphragm with dimension of 4.5 mm (width) x 18 mm (length). Detail structure of the prototype directional speaker will be introduced. Frequency response of the prototype revealed that the output sound power level (SPL) with a root mean square voltage of 10 V increased gradually to the highest peak of 93 dB for 1.5 kHz and exhibited a relatively stable behavior over the measured frequency range (?20 kHz) at a distance of 10 cm. The characteristics of total harmonic distortion (THD) was also satisfactory (< 5%). Therefore, it is considered that the prototype directional speaker is highly potential for acoustic devices such as piezoelectric speakers and transducers.

Authors : Katarzyna Olkowska1 , Daniel J. Jastrzebski2 , Patrycja Frąk1 , Cezariusz Jastrzebski1, Slawomir Podsiadlo2
Affiliations : (1) Faculty of Physics, Warsaw University of Technology; Koszykowa 75, 00-662 Warsaw, Poland (2) Faculty of Chemistry, Warsaw University of Technology; Noakowskiego 3, 00-664 Warsaw, Poland

Resume : Gallium Sulfide belongs to semiconducting materials with layered structure and characteristic weak layer-layer interaction. As a wide bandgap semiconductor it is considered as interested material for applications in electrochemistry (GaS as a material for electrodes and for catalysis in hydrogen production), optoelectronics (photodetectors, near-blue light emitting devices, gas sensor) or nonlinear optics. Because of weak van der Waals forces, GaS crystal is relatively easy to exfoliate to single layer. In this work very thin ( nano-metric ) GaS layers are obtained in mechanical and chemical exfoliation process. The layers are next transferred to Si/SiO2 substrate. The thickness of the layers is estimated from AFM measurements. Raman spectra are collected for different layer thickness. Raman position and the FWHM of the main GaS Raman peaks will be presented and discussed in comparison to the other layered semiconductors and phonon density of states.

Authors : Cezariusz Jastrzebski1, Daniel J. Jastrzebski2, Slawomir Podsiadlo2
Affiliations : (1) Faculty of Physics, Warsaw University of Technology; Koszykowa 75, 00-662 Warsaw, Poland (2) Faculty of Chemistry, Warsaw University of Technology; Noakowskiego 3, 00-664 Warsaw, Poland

Resume : Layered, two-dimensional materials are considered as the most promising for future applications in opto-electronic devices. Thermal properties of the materials are often crucial and deciding about application. Studies of phonons behavior in these materials can achieve information about their thermal conductivity. Raman scattering is one of the straightforward measurement technique for this information. Raman measurements are performed on a few nanometer in thickness SnS2 layers as a function of temperature in the range from nitrogen liquid temperature to slightly above room temperature . Different path of phonon decay in the thin layers is discussed and compared to bulk structure of SnS2. Temperature dependence of Raman shift coefficient for main Raman peak is presented. . Additional Raman spectra are analyzed in comparison to density of phonon states in these materials. Thin layers of the materials were obtained by mechanical exfoliation The obtained materials have been structurally characterized with X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy.

Authors : Benjamin J. Irving, Paolo Nicolini, Tomas Polcar
Affiliations : Czech Technical University in Prague, Czech Technical University in Prague, University of Southampton

Resume : Owing to specific characteristics engendered by their lamellar structures, transition metal dichalcogenides of general form MX2 (M = Mo, W; X = S, Se, Te) are posited as being some of the best solid-state lubricants available. Solid lubricants offer a number of advantages over their wet counterparts such as low evaporation rate, increased working temperature range and improved corrosion resistance. We have performed an extensive series of density functional theory calculations in order to investigate the sliding properties and associated phenomena of these materials.1 Specifically, we have calculated potential energy and charge transfer profiles in order to highlight the dependence of shear strength on chemical composition and bilayer orientation (sliding direction). Furthermore, our calculations highlight the intrinsic relationship between incommensurate layers and the superlubric behaviour of molybdenum disulfide. Not only do our calculations improve our understanding of the synergy between interlayer interactions and frictional behaviour, they also represent the potential predictive capabilities of in silico methods during the material design process. [1] B. Irving, P. Nicolini and T. Polcar, Nanoscale, 2017, DOI: 10.1039/C7NR00925A

Authors : Tim Theil, Yug Joshi, Guido Schmitz
Affiliations : Institute of Materials Science, University of Stuttgart Germany

Resume : Optical modulation is a necessary building block for building optics integrated circuits for computing and other optoelectronic devices. It is not extensively reported how optical properties are influenced with lithium intercalation and de-intercalation. Here the effects on four established battery electrode materials (lithium manganese oxide, lithium iron phosphate, lithium titanate and lithium cobalt oxide) are compared. The samples were characterized by in-situ optical reflectometry during charging and discharging in the wavelength range of 450-1000 nm. Therefore, the samples were prepared on oxidized silicon substrates with gold and platinum as reflective current collectors. The electrode materials are deposited by ion-beam sputtering and additional annealing treatments. The measured reflectance spectra at different charge stated are modeled by the Clausius-Mossotti dispersion relation. To fit in the measured range, the following assumptions were made: Photon electron interaction can be sufficiently described by three oscillators, light has normal incidence using Fresnel’s equation and multiple reflections are happening within the electrode material. Observations in kinetic behavior are shown for the samples and first conclusions are drawn.

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Iron based layered superconductors-II : M. Nohara
Authors : Dongjoon Song1, Shigeyuki Ishida1, Hiraku Ogino1, Akira Iyo1, Hiroshi Eisaki1,Masamichi Nakajima2,Jun-ichi Shimoyama3,Michael Eisterer4
Affiliations : 1Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan; 2Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan; 3Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara 252-5258, Japan; 4Atominstitut, TU Wien, Stadionallee 2, 1020 Vienna, Austria

Resume : The in-plane critical current density (Jc) of Ba1-xKxFe2As2 (K-Ba122), Ba(Fe1-xCox)2As2 (Co-Ba122), and BaFe2(As1-xPx)2 (P-Ba122) is investigated by magnetization hysteresis loop (MHL). Depending on the dopant and x, Jc exhibits a variety of magnetic-field (H)- and temperature (T)- dependences. (1) For K-Ba122, the MHL of the under-doped samples (x < 0.33) exhibits the second magnetization peak (SMP), which sustains high Jc at high H and high T, exceeding 105 A/cm2 at T = 25 K and µ0H = 6 T for x = 0.30. The SMP is missing in the optimally- (x ~ 0.36-0.40) and over-doped (x ~ 0.50) samples, and consequently Jc rapidly decreases by more than one order of magnitude. (2) For Co-Ba122, the SMP is present over the entire superconducting (SC) dome. However, the magnitude of Jc significantly changes with x, exhibiting a sharp maximum at x ~ 0.057 (3) For P-Ba122, the highest Jc is attained at x = 0.30 corresponding to the highest Tc composition. For the over-doped samples, the MHL is characterized by a SMP located close to the irreversibility field Hirr. Common to the three doping variations, Jc becomes highest at the under-doping side of the SC dome near the SC-AF phase boundary. The scaling analysis of the normalized pinning force density fp as a function of the reduced magnetic field h = H/Hirr (Hirr: irreversibility field) shows that the peak in the pinning force position (hmax) depends on x. Possible origins for the different pinning mechanism are discussed.

Authors : Thorsten Schmitt
Affiliations : Paul Scherrer Institut, Swiss Light Source, CH-5232 Villigen PSI, Switzerland

Resume : Resonant inelastic X-ray scattering (RIXS) is a powerful bulk-sensitive photon-in / photon-out spectro-scopic probe of the electronic structure of condensed matter with atomic and orbital sensitivity. It is a unique tool for studying excitations from the electronic ground state in correlated materials, being directly sensitive to lattice-, charge-, orbital- and spin-degrees of freedom. In this presentation we demonstrate that RIXS at the Fe L3 edge can be used to measure collective magnetic excitations in iron-based superconductors and their parent compounds. Our experiments on hole doped Ba1-xKxFe2As2 and electron doped Ba(Fe1-xCox)2As2 single crystals show well-defined spin-excitations dispersing up to 200 meV and persisting into the superconducting phase. High-energy spin-excitations in Ba(Fe1-xCox)2As2 are in agreement with NaFe1-xCoxAs independent on electron doping, in contrast to hole doped Ba1-xKxFe2As2 for which the spin excitations are clearly softening relative to parent BaFe2As2 highlighting an electron-hole asymmetry of the spin excitations. The situation is different in the BaFe2(As1-xPx)2 series for which superconductivity appears with isovalent doping without changing the number of carriers. Remarkably, the energy of the persistent broad dispersive magnetic excitations in BaFe2(As1-xPx)2 are strongly hardened by doping, arising from the decrease of electronic correlations. However, Fe-Kβ X-rays emission spectroscopy shows a gradual quenching of the local magnetic moment, which is intriguing if compared to the behavior of the spin correlations. We link this unconventional evolution of the magnetism to the shift from 2- to 3-dimensional electronic structure of the system.

Authors : Takeshi Suzuki, Shik Shin
Affiliations : Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan

Resume : FeSe has the simplest crystal structure among Fe-based high Tc superconductors and has attracted enormous interest so far. One of the intriguing features is its ability to exhibit higher Tc under extreme conditions, such as pressure, intercalation, and a few layers. Another knob includes photo-excitation, which can instantaneously control electronic and crystallographic properties without contact or processing. In this regard, time- and angel-resolved photoemission spectroscopy (TARPES) is a quite powerful tool because it can track transient band structures temporarily emerging after photo-excitation. In this talk, we would like to show our recent results on FeSe measured by the TARPES system employing high harmonic generation from Ar gas for probe pulses. We observed coherent phonon excitations after strong photo-excitation, and would like to discuss the accompanying photo-excited electronic states by comparison with band structure calculations.

Authors : Yoshihiko Takano and Ryo Matsumoto
Affiliations : National Institute for Materials Science (NIMS), Tsukuba Univ.

Resume : Superconductivity under high pressure has been paid the considerable attention. In particular superconductivity in H2S at 200 K under 150 GPa was discovered using a diamond anvil cell (DAC) [1]. It is predicted that if we can measure the resistivity under extremely higher pressure above 300 GPa, superconductivity at room temperature in hydrogen could be observed [2]. However, resistivity measurement under high pressure is quite difficult because of the small sample sizes (< 100 μm) and the deformation of electrodes by compression. The development of an innovative technique for the transport measurements under high pressure is required. In this study, we have developed a DAC specialized for the resistivity measurements under high pressure [3]. The key component is a special diamonds. It is a heavily boron-doped metallic diamond as an electrode [4,5]. When the boron concentration exceeds 3×10^20 cm-3, diamond shows metallicity and superconductivity at low temperature. The diamond electrodes were nanofabricated by using combination of a microwave-assisted plasma chemical vapor deposition method and an electron beam lithography technique. We have performed a pressure effects of Tc for several superconductors including Fe-based superconductors and High-Tc superconductors. In my presentation, I will give a talk about detailed results of physical properties under pressure. References 1. A. P. Drozdov, M. I. Eremets, I. A. Troyan, V. Ksenofontov and S. I. Shylin, Nature 525, 73(2015). 2. N. W. Ashcroft, Phys. Rev. Lett. 21, 1748 (1968). 3. R. Matsumoto, Y. Sasama, M. Fujioka, T. Irifune, M. Tanaka, T. Yamaguchi, H. Takeya and Y. Takano, Review of Scientific Instruments 87, 076103 (2016) 4. Y. Takano, M. Nagao, I. Sakaguchi, M. Tachiki, T. Hatano, K. Kobayashi, H. Umezawa and H. Kawarada, Appl. Phys. Lett. 85, 2851 (2004). 5. T. Yokoya, T. Nakamura, T. Matsushita, T. Muro, Y. Takano, M. Nagao, T. Takenouchi, H. Kawarada and T. Oguchi, Nature 438, 647 (2005).

10:30 Coffee break    
Bismuth based layered dichalcogenides : T. Yokoya
Authors : Yuji Aoki, Ryuji Higashinaka, Tatsuma D. Matsuda
Affiliations : Department of Physics, Tokyo Metropolitan University, Tokyo, Japan

Resume : BiS2-based layered superconductors Ln(O,F)BiS2 (Ln: rare earth), which consist of alternating stacking of BiS2 conductive layers and LnO block layers have been attracting much attention [1]. Since 4f electrons of Ln ions in the block layers have magnetic degrees of freedom, it is an intriguing question whether the magnetism and superconductivity compete or coexist in this material. We have succeeded in growing high-quality single crystals of Ln(O,F)BiS2 series and have been investigating 4f-electron behaviors. Here we report recent findings of unconventional 4f-electron magnetism in this series [2]. In CeOBiS2, 4f-electrons has a energetically-well-separated doublet ground state and it shows a pronounced -logT divergence in the specific heat at low temperatures [2]. Considering that CeOBiS2 is a nonmetal, this phenomenon cannot be attributed to the competition between Kondo and RKKY interactions as in usual f-electron-based strongly correlated metals, pointing to an unconventional mechanism working in this material. Similar anomaly appears also in Nd(O,F)BiS2. A possible role played by the characteristic feature in the layered crystal structure is discussed. [1] Y. Mizuguchi et al., J. Phys. Soc. Jpn. 81, 114725 (2012). [2] R. Higashinaka et al., J. Phys. Soc. Jpn., 84, 023702 (2015).

Authors : Yoshikazu Mizuguchi
Affiliations : Tokyo Metropolitan University, 1-1, Minami-osawa, Hachioji, Japan.

Resume : Since 2012, superconductors with BiCh2 layers (Ch: S, Se) have been drawing much attention as a new class of layered superconductors, because of structural similarity to the cuprates and Fe-based family [Y. Mizuguchi et al., JPSJ 2012; PRB 2012]. We have investigated the effects of carrier doping and crystal structure tuning to the superconducting properties of BiCh2-based compounds. We have revealed the essential correlation between superconductivity and in-plane chemical pressure in the conductive Bi-Ch square lattice [Y. Mizuguchi et al., Sci. Rep. 2015]. Furthermore, we have recently reported that the importance of local structural disorder at the in-plane Ch site was strongly correlating with the emergence of superconductivity in the BiCh2 layer [K. Nagasaka et al. JPSJ 2017]. In this presentation, we will review the essential conditions required for the emergence of superconductivity in BiCh2-based compounds. In addition, we will show the crystal structure and physical properties of several new BiCh2-based compounds, which have been recently discovered.

Authors : M. A. Griffith, T. P. Oliveira, M. A. Continentino, G. B. Martins
Affiliations : Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, Urca, 22290-180 Rio de Janeiro, RJ, Brazil; Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, Urca, 22290-180 Rio de Janeiro, RJ, Brazil; Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, Urca, 22290-180 Rio de Janeiro, RJ, Brazil; Instituto de Fisica, Universidade Federal Fluminense, 24210-346 Niteroi, RJ, Brazil.

Resume : A mean-field treatment is presented of a square lattice two-band-model for BiS2 taking into account intraband and interband superconductivity. A rich phase diagram involving both types of superconductivity is presented as a function of the ratio between couplings \eta= V_{XX}/V_{XY} and electron doping x. With the help of a quantity we call band-mixing ratio, denoted as R(\phi), the phase diagram is analyzed using a simple and intuitive picture based on how $R(\phi)$ varies as electron doping increases. The predictive power of $R(\phi)$ suggests that it could be a useful tool in qualitatively (or even semi-quantitatively) analyzing multiband superconductivity in BCS-like superconductors.

Authors : Takanori Wakita, Kensei Terashima, Takahiro Hamada, Hirokazu Fujiwara, Makoto Minohara, Masaki Kobayashi, Koji Horiba, Hiroshi Kumigashira, Galif Kutluk, Masanori Nagao, Satoshi Watauchi, Isao Tanaka, Satoshi Demura, Hiroyuki Okazaki, Yoshihiko Takano, Yoshikazu Mizuguchi, Osuke Miura, Kozo Okada, Yuji Muraoka, and Takayoshi Yokoya
Affiliations : Research Institute for Interdisciplinary Science, Okayama University, Okayama 700-8530, Japan, Photon Factory, Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan, Synchrotron Radiation Center, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-0046, Japan, Center for Crystal Science and Technology, University of Yamanashi, Kofu, Yamanashi 400-8511, Japan, National Institute for Materials Science, Sengen, Tsukuba 305-0047, Japan, Department of Electrical and Electronic Engineering, Tokyo Metropolitan University, Minami-osawa, Hachioji 192-0397, Japan, Department of Physics and the Graduate school of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.

Resume : We use soft x-ray photoemission spectroscopy (SXPES) to investigate Ce 4f electronic states of a new BiS2 layered superconductor CeO1−xFxBiS2, for polycrystalline and single-crystal samples. The Ce 3d spectrum of the single crystal of nominal composition x = 0.7 has no f0 component and the spectral shape closely resembles the ones observed for Ce trivalent insulating compounds, strongly implying that the CeO layer is still in an insulating state even after the F doping. The Ce 3d-4f resonant SXPES for both polycrystalline and single-crystal samples shows that the prominent peak is located around 1 eV below the Fermi level (EF) with negligible spectral intensity at EF. The F-concentration dependence of the valence band spectra for single crystals shows the increases of the degeneracy in energy levels and of the interaction between Ce 4f and S 3p states. These results give insight into the nature of the CeO1−xFx layer and the microscopic coexistence of magnetism and superconductivity in CeO1−xFxBiS2.

12:30 Lunch break    
Layered cuprates and iridates : D. Mihailovic
Authors : M. Oda,T. Kurosawa,S. Mizuta,T. N. Momono, K. Takeyama, H. Yoshida and M. Ido
Affiliations : Department of Physics, Hokkaido Univ., Sapporo, Japan; Department of Applied Science, Muroran Institute of Technology, Muroran, Japan; Department of Physics, Asahikawa Medical Univ., Asahikawa, Japan

Resume : We report STM/STS studies in underdoped (UD) and optimally (OP) doped crystals of Bi-based high-Tc cuprate Bi2212. In many cases of STM/STS experiments on UD Bi2212 crystals, we observe STS spectra consistent with a two-gap structure consisting of a d-wave SC gap (SCG) and a spatially inhomogeneous pseudogap (PG), whose size varies in nanometer scale over a wide range from an energy of the SCG amplitude to several times larger one. In such UD crystals, we demonstrate checkerboard modulation (CBM) and Cu-O-Cu bond-centered modulation (BCM), which are observed in conductance images at low energies around the SCG and high energies around the PG, respectively; the two electronic superstructures with different characteristic energies coexist with each other in real space. On the other hand, no CBM and BCM are observed in STM/STS experiments on some cleaved surfaces of OP Bi2212; STS spectra exhibit a homogeneous single d-wave like SCG structure within the areas examined. In such OP crystals, we demonstrate that the overall SCG on the entire Fermi surface spatially changes with an amplitude of ~6% of its average and the same period as in the one-dimensional superlattice, which has been predicted by theoretical studies to cause periodic modulation of the antiferromagnetic coupling between Cu-spins.

Authors : T. Adachi^1^, T. Sumura^1^, M. A. Baqiya^2^, A. Takahashi^2^, T. Konno^2^, T. Ohgi^2^, K. Ohashi^2^, K. Kurashima^2^, T. Kawamata^2^, T. Ishimoto^1^, H. Kuwahara^1^, I. Watanabe^3^, A. Koda^4^, M. Miyazaki^5^, R. Kadono^4^, S. Awaji^6^ and Y. Koike^2^
Affiliations : ^1^ Department of Engineering and Applied Sciences, Sophia University, Tokyo, Japan ^2^ Department of Applied Physics, Tohoku University, Sendai, Japan ^3^ Advanced Meson Science Laboratory, RIKEN Nishina Center, Wako, Japan ^4^ Muon Science Laboratory, Institute of Materials Structure Science, KEK, Tsukuba, Japan ^5^ Graduate School of Engineering, Muroran Institute of Technology, Muroran, Japan ^6^ Institute for Materials Research, Tohoku University, Sendai, Japan

Resume : Our recent transport and muon-spin-relaxation (muSR) results of the electron-doped high-T_c_ cuprates with the so-called T' structure are reviewed in relation to the undoped (Ce-free) superconductivity in the parent compounds [1-3]. The Hall resistivity of the reduced single crystals of Pr_2-x-y_La_y_Ce_x_CuO_4+d_ (PLCCO) has revealed a nonlinear (linear) behavior in magnetic field in the superconducting (non-superconducting) crystals, suggesting the existence of multiple carriers in the superconducting crystals. The muSR time spectra of reduced superconducting PLCCO with x = 0.10 and y = 0.7 have revealed the development of the Cu-spin correlation at low temperatures. Moreover, the development of the Cu-spin correlation has been found to weaken with increasing x and almost disappear at the end point of the superconducting region in the phase diagram. These results suggest that the multiple carriers and developed Cu-spin correlation are crucial to appear the superconductivity in the T’-cuprates. For the parent compound of undoped La_1.8_Eu_0.2_CuO_4+d_, impurity substitution for Cu has uncovered the superconducting pairing symmetry as a d-wave one. These results are understandable in terms of our proposed novel electronic-structure model based on the strong electron correlation. [1] T. Adachi et al., J. Phys. Soc. Jpn. 82, 063713 (2013). [2] K. Ohashi et al., J. Phys. Soc. Jpn. 85, 093703 (2016). [3] T. Adachi et al., J. Phys. Soc. Jpn. 85, 114716 (2016).

Authors : K. Terashima, M. Sunagawa, H. Fujiwara, T. Fukura, M. Fujii, K. Okada, K. Horigane, K. Kobayashi, R. Horie, J. Akimitsu, E. Golias, D. Marchenko, A. Varykhalov, N. L. Saini, T. Wakita, Y. Muraoka, and T. Yokoya
Affiliations : Research Institute for Interdisciplinary Science, Okayama University, Okayama, 700-8530, Japan, Graduate School of Natural Sciences, Okayama University, Okayama, 700-8530, Japan, Aoyama Gakuin University, Sagamihara, kanagawa 229-8558, Japan, Helmholtz-Zentrum Berlin fu ̈r Materialien und Energie, Albert-Einstein-Str. 15, 12489 Berlin, Germany, Dipartimento di Fisica, Universita ́ di Roma “La Sapienza” - P. le Aldo Moro 2, 00185, Roma, Italy

Resume : Sr2IrO4 crystalizes in K2NiF4-type structure and is an antiferromagnetic insulator with TN = 240 K, whose character has been recognized as a consequence of large spin-orbit interaction as well as Coulomb interaction in Ir 5d electrons. Recent observations of anisotropic energy gap in carrier-doped samples [1,2] provided experimental support to theoretical claims that doped Sr2IrO4 can be a superconductor, while little is known about how this state evolves from parent insulating compound [3]. In order to clarify this point, we have performed angle-resolved photoelectron spectroscopy on lightly-doped (Sr,La)2IrO4 single crystals. We have found that a dispersive state develops inside the Mott gap by La doping, whose momentum dependence corresponds to the d-wave gapped state at higher doping [2] but its energy position is altered by the presence of anistropic gap, resulting in a remnant Fermi surface state. These observations suggest that the nodal liquid state observed in higher-doped Sr2IrO4 samples evolves in a highly corresponding manner as in cuprate superconductors. [1] Y. K. Kim et al., Nature Physics 12, 37 (2015) [2] A. de la Torre et al., Phys. Rev. Lett. 115, 176402 (2015) [3] V. Brouet et al., Phys. Rev. B 92, 081117(R) (2015)

Authors : E. Paris, D.E. McNally, Y. Tseng, M. Radovic, T. Schmitt
Affiliations : Paul Scherrer Institut, Swiss Light Source, CH-5232 Villigen PSI, Switzerland

Resume : The Sr2IrO4 material has been in the lime light during last years due to the discovery of a novel Jeff = ½ Mott state in the large spin-orbit regime. The sensitivity of this quantum state to local coordination and structural distortions suggests strain and confinement as ideal routes for studying and manipulating its properties. Recently, it was demonstrated that oxygen K-edge resonant inelastic X-ray scattering (RIXS) is capable to capture magnetic excitations in 5d-oxides [1]. Due to the higher surface sensitivity compared to the hard X-ray counterpart, the soft X-ray RIXS is the most suitable for the investigation of thin films. From O K-edge RIXS on roughly 20 nm-thick Sr2IrO4 films, grown on several substrates by Pulsed Laser Deposition (PLD), we detected the low-energy elementary excitations encompassing single magnons, bimagnons and spin-orbital excitations and their dispersion relations as a function of strain. In this talk, I will present a direct observation of the evolution of these low-energy quasiparticle excitations and the spin dynamics upon epitaxial strain in the Jeff = ½ Mott insulator Sr2IrO4. [1] X. Lu et al, “Oxygen K-edge Resonant Inelastic X-Ray Scattering as a Probe of Single Magnons and Excitonic Quasiparticles in Sr2IrO4 and Sr3Ir2O7”, manuscript submitted

15:30 Coffee break    
Iron based layered superconductors-III : H. Eisaki
Authors : Kazuhiko Kuroki
Affiliations : Department of Physics, Osaka University

Resume : A unique iron-based superconductor FeSe and related materials have attracted much attention lately. One of the interesting features of FeSe is the effect of the excess irons. There are actually several possibilities for the effect : carrier doping, appearance of impurity bands, or affecting the original band structure itself. Here we have performed a band calculation of FeSe and related materials using a supercell that contains the excess iron, and then unfolding the band structure to compare with the original one. We find that all of the above three effects take place, depending on the quantity of the excess irons. We will discuss these effects in detail.

Authors : M. Capone, L. de' Medici, L. Fanfarillo. G. Giovannetti
Affiliations : SISSA and CNR-IOM, Trieste (M. C., L.F. and G.G. ) and ESPCI, Paris (L. d.M.)

Resume : The strength and the role of electron-electron correlations in iron-based superconductors remain debated. We argue that solution of the debate lies in the orbital-selective character of the correlations, with some orbitals being significantly more correlated than others. This reconciles conflicting evidences and accounts for the dependence of the effective mass on doping and on the specific material considering the cases of electron- and hole-doped BaFe2As2 [1] and the comparison between FeSe and FeS [2]. The orbital-selective Mott scenario also establishes a novel link between the iron-based superconductors and the cuprates, which suggests that the role of electron-electron correlations may be also the source of superconductivity. In this perspective in the second part of the talk we also discuss how such orbital-selective correlations influence the tendency towards a nematic ordering in FeSe and in other compounds [3] and the role of selective correlations in determining the properties and the symmetry of the superconducting state [4]. [1] L. de' Medici, G. Giovannetti and M. Capone, Phys. Rev. Lett. 112, 177001 (2014) [2] L. Fanfarillo. G. Giovannetti, M. Capone and E. Bascones, Phys. Rev. B 95, 144511 (2017) [3] C. Tresca, G. Giovannetti, M. Capone and G. Profeta, Phys. Rev B 95, 95, 205117 (2017) [4] L. Fanfarillo, A. Valli and M. Capone, in preparation

Authors : T. Nojima, J. Shiogai, T. Miyakawa, Y. Ito, and A. Tsukazaki
Affiliations : Institute for Materials Research, Tohoku University

Resume : The superconductivity in the thin limit or at the interface has been a new trend to explore novel quantum phenomena, which are accelerated by the discovery of high transition temperature (Tc) superconductivity above 40 K in monolayer FeSe on SrTiO3. It has been proposed so far that the high Tc superconductivity originates from the interfacial effects between the film and substrate including electronic band modulation, charge transfer, and electron-phonon coupling. However, what effect plays a central role is still under devate. In this talk, we introduce that the multi-functionalities of electric double layer transistor, containing electrochemical etching and electrostatic doping, provide a new route to study the thin film or interfacial superconductivity [1], and then demonstrate our systematic studies on the high Tc superconductivity of FeSe as a function of thickness, substrate material, and electric field [2]. The maximum value of the onset Tc reaches 40 K for all the FeSe on various substrates, such as SrTiO3, MgO and KTaO3, with thinning. In addition, we found a universal relationship between the Hall coefficient in normal state and Tc regardless of different film thickness and substrate materials. The finding evidences that the high-Tc superconductivity does not primarily originate from a specific interface combination but from a charge carrier filling at specific electronic band structure. We will also discuss how the superconductivity develops using the estimated length scales of charge accumulation layers at the Ionic liquid/FeSe and FeSe/substrate interfaces. [1] J. Shiogai et al., Nat. Phys. 12, 42 (2016). [2] J. Shiogai et al., Phys. Rev. B 95, 115101 (2017).

Authors : B. Kalska-Szostko1, U. Klekotka1, E. Wińska1, E. Zambrzycka-Szelewa1, D. Satuła2,
Affiliations : 1Institute of Chemistry, University of Bialystok, Ciolkowskiego 1K, 15-245, Bialystok Poland 2Faculty of Physics, University of Bialystok, Ciolkowskiego 1L, 15-245, Bialystok, Poland

Resume : Nowadays, environmental pollution is a very hot topic. Contamination of the environment and therefore food with heavy metals is one of the most urgent subject among scientists. That is why, presented studies refers to the tests on the extraction of heavy metal ions (Pb2+, Cu2+, Cd2+) from aqueous samples by means of surface functionalized ferrite nanoparticles doped with calcium, cobalt, nickel and manganese. In order to increase the extraction of the heavy metals, nanoparticles surface was modified with five different ligands (phthalic anhydride, succinic anhydride, acetic anhydride, 3-phosphonopropionic acid, and 16-phosphonohexadecanoic acid). Aqueous samples after extraction were examined by FAAS method. Nanoparticles with and without attached ions have been tested with EDX. Inorganic ferrite cores used for tests, firstly were characterized by physicochemical methods (TEM, X-ray diffraction, IR spectroscopy, and Mössbauer spectroscopy). It is shown that surface modification of nanoparticles can significantly influence on the extraction of tested heavy metal ions and the effectiveness is related not only to surface modification but also to core composition. The work was partially financed by EU founds via project with contract number POPW.01.03.00-20-034/09-00, POPW.01.03.00-20-004/11-00 and by NCN founds, project number 2014/13/N/ST5/00568.

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09:00 Plenary Session - Main Hall    
12:30 Lunch break    
Layered superconducting chalcogenides and related materials : Y. Takano
Authors : Kenya Ohgushi1, Yasuyuki Hirata2, Touru Yamauchi2, Fei Du3, Yutaka Ueda4, Yusuke Nambu5, Maxim Avdeev6, Taku J. Sato7, Akira Sugimoto8, Chizuru Kawashima8, Hideto Soeda8, and H. Takahashi8
Affiliations : 1Department of Physics, Tohoku University, Japan; 2Institute for Solid State Physics, University of Tokyo, Japan; 3College of Physics, Jilin University, China; 4Toyota Physical and Chemical Research Institute, Japan; 5Institute for Materials Research, Tohoku University, Japan; 6Bragg Institute, Australian Nuclear Science and Technology Organisation, Australia; 7Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan; 8College of Humanities & Sciences, Nihon University, Japan

Resume : All the iron-based superconductors identified so far share a square lattice composed of iron atoms as a common feature. In copper-based high-Tc materials, the superconducting phase emerges not only in square-lattice structures but also in ladder structures, which give nice hints for elucidating the microscopic mechanism of the superconductivity. Here, we report the discovery of pressure-induced superconductivity in the iron-based ladder material BaFe2S3, a Mott insulator with striped-type magnetic ordering below 120 K. On the application of pressure, this compound exhibits a metal–insulator transition at about 11 GPa, followed by the appearance of superconductivity below Tc = 24 K. Our findings indicate that the square lattice is not the necessary ingredients of the superconductivity and that not only the spin and orbital fluctuations but also the charge fluctuations could play a key role in the emergence of the superconductivity in iron-based superconductors. [1] Y. Nambu, et al., Phys. Rev. B 85, 064413 (2012). [2] F. Du, et al., Phys. Rev. B 85, 214436 (2012). [3] F. Du, et al., Phys. Rev. B 90, 085143 (2014). [4] D. Ootsuki, et al., Phys. Rev. B 91, 014505 (2015). [5] T. Hawai, et al., Phys. Rev. B 91, 184416 (2015). [6] H. Takahashi, et al., Nat. Mater. 14, 1008 (2015). [7] Y. Hirata, et al., Phys. Rev. B 92, 205109 (2015). [8] T. Yamauchi, et al., Phys. Rev. Lett. 115, 246402 (2015). [9] Songxue Chi, et al., Phys. Rev. Lett. 117, 047003 (2016). [10] Kou Takubo, et al., arXiv:1704.04864.

Authors : Masashi Tanaka, Hiroyuki Takeya, Yoshihiko Takano
Affiliations : Graduate School of Engineering, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata, Kitakyushu 804-8550, Japan; MANA, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan

Resume : Layer structured iron selenide, FeSe has the simplest crystal structures among iron-based superconductors. It shows superconductivity with transition temperature (Tc) around ~10 K under ambient pressure. When potassium is intercalated between FeSe layers, the Tc increases more than 30 K, and it has been reported as potential superconductors with Tc’s of 30-48 K. However, the intercalated crystals, KxFe2-ySe2 intrinsically separate into superconducting 122-phase and insulating 245-phase. Then it has been had difficulties for the identification of the relationship between the surface morphology, compositional ratio and its crystal structure. We have been investigated growth mechanism and superconducting properties of the single crystals using In-situ high-temperature single crystal X-ray diffraction measurements [1] and TEM measurements supported by a micro-sampling technique [2]. These diffraction studies directly revealed the effect of heating treatment and correspondence between compositional ratio and the crystal structure. Finally, it was concluded that a perfect FeSe layers in the crystals provides the higher Tc superconducting phase of ~44 K. References [1] M. Tanaka et al. J. Phys. Soc. Jpn., 85, 044710 (2016). [2] M. Tanaka et al. Appl. Phys. Express, 10, 023101 (2017).

Authors : Tong Zhang
Affiliations : Department of physics, Fudan University, Shanghai, China

Resume : Recently enhanced superconductivity (SC) in single-layer FeSe/STO (Tc > 65 K) [1] and electron doped FeSe (Tc >40K) was observed. Here, I will present STM study on the pairing symmetry of FeSe/STO [2] and Li0.8Fe0.2OHFeSe [3]. We studied SC state and the pairing symmetries by field dependent quasi-particle interference (QPI). The result suggests plain s-wave pairing, without phase change. Substrate effects and doping dependence will also be presented [4]. We compare the SC in FeSe films grown on SrTiO3 and graphitized SiC. The results indicate that FeSe/SrTiO3 interface can further enhance SC beyond mere doping. The enhancement decays exponentially with thickness, pointing to interfacial electron−phonon coupling. Besides, we studied the electronic structure and SC of (Li, Fe)OHFeSe via surface K-dosing. We found that the Γ-centered electron band can be tuned to cross EF by K-dosing, resulting in a Lifshitz transition. With further K -dosing, a new SC dome emerges on the Γ-pocket. Eventually, the system evolves in to an anomalous insulating phase with gradually depleted DOS near EF. Our results provide clues to understand FS topology vs. SC, and reveal the anomalous correlation effect derived SC. [1]. Q. Wang, et al., Chin. Phys. Lett. 29, 037402 (2012). [2]. Q. Fan, et al., Nat. Phys. 11, 946 (2015). [3]. Y. J. Yan, et al, Phys. Rev. B 94, 134502 (2016). [4]. W.H. Zhang, et al, Nano Lett., 16, 1969 (2016).

Authors : Kaya Kobayashi, Teppei Ueno, Jun Akimitsu
Affiliations : RIIS Okayama University; Physics Department Okayama University; RIIS Okayama University

Resume : Cubic chalcogenide, SnTe has been attracting interest after presenting the possibility of a topological crystalline insulator. Doping In achieved the highest transition temperature (Tc) superconductivity. Surface sensitive spectroscopy revealed that Sn1-xInxTe shows topologically protected unique surface states. This interest brought the material family of SnTe into the intensive studies, such as alloy compound with Pb, Pb1-xSnxTe. In doped superconductors drew attention due to the limited valence state Sn, Pb and In show. In pursuit of new cubic superconductor with the unique surface state, we focused on one of the candidate materials, Ag1-xSn1+xSe2.   We investigated the properties, mostly lattice constant and Tc by substituting Se site for other chalcogens, Te and S. The obtained result indicates that the fundamental behavior stays unchanged by the chalcogen substitution, while the correlation between the lattice constant and Tc does not fall onto a single curve in chalcogen substitution. This indicates that the relation between these two parameters indicates the superconductivity is governed by Ag/Sn site rather than chalcogen sites. The substitution of Se also gives a slight modulation on Tc, which is expected from the similarity to SnTe where the bands at the Fermi energy consist of both Sn and Te. In contrast to the Se site substitution, substitution of Ag/Sn site by numerous elements gives a single curve when Tc is plotted against the ratio of Sn2+ and chalcogen. While there are several findings of the valence of elements, the behavior indicates that the Sn2+ is the key parameter for defining the superconductivity, which contrasts from other SnCh superconductors.

Authors : Andrei POSTNIKOV (1), Michael BADAWI (1), Sébastien LEBÈGUE (2)
Affiliations : (1) LCP-A2MC - Institut Jean Barriol, Université de Lorraine; (2) CRM2 - Institut Jean Barriol, Université de Lorraine

Resume : A number of structural models are under discussion for the In2Se3 semiconductor, based on its crystallographic studies and in the context of previous first principles calculations - see, e.g., [1,2]. A way to match the stoichiometry with the covalent (typically 4-coordinated) bonding can be found within either (i) a bulk crystal containing (ordered) cation vacancies, or (ii) a layered structure, that offers, in its turn, variations in layer stackings and nearest-neighbour coordinations. For practical / predictive applications, the issues of correct representation of the dispersive interactions (hence getting accurate interatomic distances) and of the correct description of the optical gap (in order to adequately simulate electron excitations) are of primary importance. Keeping an affordable computational effort as a relative priority, we probe schemes (variations of those by Grimme and Tkatchenko - Scheffler), to take into account the van der Waals interaction, in view of making reliable predictions of total energies and the precision lattice relaxations. Moreover we compare the performance of the mBJ (meta-GGA) vs the HSE (hybrid) exchange-correlation potentials within the density-functional theory in what concerns the description of the electron bands. For some phases which are competitive in energy, a connecting structural path will be suggested, and the vibration-related corrections to the static total energies estimated. [1] L.Debbichi et al., J.Phys.Chem.Lett.6, 3098 (2015); [2] J.Srour et al., Phys.Stat.Sol.B (2017); DOI 10.1002/pssb.201700120

15:45 Coffee break    
Layered functional materials : Y.-W. Son
Authors : Christos Panagopoulos
Affiliations : Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore

Resume : I will discuss our coherent effort in Singapore to modulate the properties of multilayer architectures for functional skyrmion devices at room temperature. First, I will introduce a materials recipe to tune the skyrmion size and density, thermodynamic stability parameter, as well as the crossover between isolated and disordered-lattice configurations. Second, I will present results on the electrical signature of skyrmions using transport and imaging experiments, and their spin dynamics and collective spin excitation modes from high frequency measurements. Finally, I will address their nucleation, stability, current-induced formation and dynamics in design-nanostructures.

Authors : Siddharth S Saxena
Affiliations : Quantum Matter, Cavendish Laboratory, University of Cambridge

Resume : In this work we show that by manipulating the lattice of incipient ferroelectrics we are able to directly control the quantum criticality in this system. Pressure is the ?applied external field? that couples directly to the lattice and its excitations - phonons. We use pressure to tune the strength of quantum critical fluctuations in incipient ferroelectrics, as well as the quantum paraelectric state and observe the evolution of a novel phase emergent from the quantum critical point. We have carried out unprecedented measurements of the dielectric response of a quantum critical ferroelectric to extremely high precision. The study of quantum criticality in ferroelectric systems is of significance as they provide a model system for the fundamental mechanisms of quantum criticality, without the complications of gapless electrons. Also recent understanding of superconductivity in interfacial systems and doped ferroelectrics has been attributed to the ferroelectric quantum criticality.

Authors : Ritsuko Eguchi^1,2, Margherita Boselli^2, Adrien Waelchli^2, Stefano Gariglio^2, Jean-Marc Triscone^2
Affiliations : 1. Research Institute for Interdisciplinary Science (RIIS), Okayama University, 700-8530 Okayama, Japan; 2. DQMP, Department of Physics, University of Geneva, 1211 Geneva, Switzerland

Resume : The superconducting state of doped SrTiO3 is somehow unique: it appears at the lowest carrier concentration in a material close to a ferroelectric order. Recent work has investigated the influence of ferroelectric fluctuations on superconductivity [1]. This theoretical study predicts an enhancement of the superconducting transition temperature (Tc) for samples in the vicinity of the ferroelectric quantum critical point (QCP). Experimental studies in ferroelectric SrTi18O3 [2] and Sr1-xCaxTiO3 (0.002 < x < 0.02) [3] have indeed revealed that Tc is higher for 18O and Ca-doped SrTiO3 samples. In this study, we investigate superconductivity at LaAlO3/Sr1-xCaxTiO3 interfaces to clarify how the 2D electron liquid at the interface is affected by the ferroelectric QCP. A clear metallic behavior is observed in SrTiO3 (6 u.c.)/LaAlO3 (5 u.c.)/Sr1-xCaxTiO3 (x = 0.005 and 0.01) heterostructures, with sheet resistance values similar to the ones of the LaAlO3/SrTiO3 system. We will discuss the superconducting properties of the LaAlO3/Sr1-xCaxTiO3 interfacial system under field effect. References: [1] J. M. Edge et al, Phys. Rev. Lett., 115 (2015) 247002., [2] A. Stucky et al., Sci. Rep. 6 (2016) 37582., [3] C. Rischau et al., Nat. Phys. 4085 (2017). DOI: 10.1038/NPHYS4085.

Authors : Yug Joshi, Efi Hadjixenophontos, Guido Schmitz
Affiliations : Institut für Materialwissenschaft, Lehrstuhl Materialphysik (IMW) University of Stuttgart,

Resume : Extensive research has been carried out in the field of optoelectronic materials and devices. In this study, intercalation of lithium ions is used to manipulate the optical response of lithium manganese oxide (LMO) films, a material normally used as cathode in secondary batteries. To study the optical behaviour, firstly platinum, a current collector, followed by the active LMO layer is deposited on oxidised silicon wafers using ion-beam sputtering. The multi-layered sample is characterized using optical reflectometry at different lithiation states of the LixMn2O4 layer between x=0 to x=1. The reversibility of the optical response is verified by in-situ optical reflectometry during charging and discharging cycles of LMO in the wavelength range of 450-1000 nm. Furthermore, the changes in the optical constants between different charge states is revealed by fitting the reflectance data with Clausius-Mossotti dispersion relation. The equation to fit the curve considers (1) three oscillators to simulate the photon-electron interaction, (2) Fresnel’s equations for normal incidence and (3) multiple reflections experienced by light in the thin film samples. The study reveals a reversible change of the optical properties during an electrochemical reaction, making it a promising candidate for the application of optical switching via phase modulation. The kinetics of switching is evaluated.

18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    
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Spectroscopy of layered systems : C. Kim
Authors : Jae-Kap Lee
Affiliations : Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea

Resume : Graphene has enormous potential due to its outstanding physical properties compared even to single-wall carbon nanotubes. One of the fundamental issues is identifying layers of graphene structures. High-resolution TEM (HRTEM) images revealing edge lines of planar view graphene provide uncontroversial evidence of the presence pure graphene. Due to the difficulty and the limitation of HRTEM observation, Raman approaches (e.g. shape of 2D-peak or an intensity ratio of 2D-peak to G-peak, I2D/IG) have been suggested as effective method for confirming graphene layers. However, the Raman data do not provide direct evidence of graphene because the shape of 2D-peak for monolayer graphene has been reported to be similar to those for multilayer graphene and the intensity ratio is an indication of electronic decoupling of graphene layers. In this presentation, a simple methodology to analyse graphene structures using Raman signals in the range ~100-~500 cm-1 will be reported. The low energy signals on Raman spectra of plasma seeded grown graphene sheets are originated from nano-curvature of mono- and bilayer graphene [1]. I will explain the appearance of the low energy Raman signals from curved graphene with radial mode (RM) of Raman Eigen vectors. The RM based new analysis provides a standard way of identifying and evaluating mono- and bilayer graphene with Raman spectroscopy. [1]. J.-K. Lee et al., The Journal of Physical Chemistry Letters. 8, 2597-2601 (2017).

Authors : Ming Shi
Affiliations : Paul Scherrer Institute, CH-5232 Villigen, Switzerland

Resume : The studies of iron-pnictides have shown that the multi-orbital low energy electronic states formed in the FeAs layer are moderately correlated due to finite Hund's coupling and on-site Coulomb interaction. However, so far, only little is known about the influence of the spacer layer on the low energy electronic states of the FeAs layer. Using angle-resolved photoemission spectroscopy, supported with DFT calculations, we determined the electronic structure of 112 Fe-pnictide Ca1-xLaxFeAs2 which has a metallic spacer layer between FeAs planes from which the superconductivity originates. Our studies reveal that, comparing to other superconducting iron-pnictides with insulating spacer layers the electron-electron correlations are not weakened by the metallic spacer layers. Furthermore, due to spin-orbit coupling the electronic structure of each CaAs layer is topologically non-trivial. These results indicate that below superconducting transition temperature Ca1-xLaxFeAs2 could be an alternating combination of a quantum spin Hall insulator and a superconductor.

Authors : X. J. Zhou
Affiliations : National Lab for Superconductivity, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

Resume : In this talk, I will present our recent work on high temperature cuprate superconductors, the iron-based superconductors, and topological materials by using vacuum ultra-violet laser-based angle-resolved photoemission systems. These include: (1). Quantitative determination of pairing interactions in high temperature cuprate superconductors[1]; (2). Common electronic structures and superconducting gap structure in (Li,Fe)OHFeSe, AxFe2-ySe2 and single-layer FeSe/SrTiO3 superconductors[2]; (3). Direct evidence of interaction-induced Dirac cones in single-layer silicene/Ag(111)[3]; (4). Temperature-induced Liftshitz transition in ZrTe5 and HfTe5 and their topological nature[4]; and (5). Spectroscopic evidence of type-II Weyl semimetal states in WTe2[5] and MoTe2[6]. References [1]. J. M. Bok, X. J. Zhou et al., Science Advances 2, e1501329 (2016). [2]. L. Zhao, X. J. Zhou et al., Nature Communications 7, 10608 (2016). [3]. Y. Feng, X. J. Zhou et al., PNAS 133, 14656 (2016). [4]. Y. Zhang, G. D. Liu, X. J. Zhou et al., Nature Communications 8, 15512 (2017). [5]. C. L. Wang, G. D. Liu, X. J. Zhou et al., Phys. Rev. B 94, 241119(R) (2016). [6]. A. J. Liang, X. J. Zhou et al., arXiv:1604.01706.

10:40 Coffee break    
Theoretical studies of layered systems : M. Capone
Authors : Philipp WERNER
Affiliations : Department of Physics, University of Fribourg, Fribourg, Switzerland

Resume : We use static Hartree-Fock, time-dependent mean-field and nonequilibrium GW calculations to investigate the response of excitonic insulators to photo-excitation. The Hartree-Fock calculations suggest that the Hartree shifts associated with the charge transfer between bands can lead to more resonant states and a transient enhacement of excitonic order after photo-excitation, in agreement with recent experimental observations [1]. The simulation of the dynamics within time-dependent mean field theory furthermore shows that the coupling to phonons may play an additional important role [2], since it produces a mass for the phase mode. The resulting dynamics is thus qualitatively different from the system without phonon coupling, and substantial photo-induced enhancements of the order can be realized. While the transient state is protected by the relatively slow carrier relaxation across the gap, the thermalization will lead to a reduction or melting of the excitionic order. We study this thermalization process using nonequilibrium GW calculations and show that it involves two stages, a slow prethermalization controlled by a nonthermal fixed point, followed by a faster thermalization [3]. [1] S. Mor et al., arxiv (2016) [2] Y. Murakami, D. Golez, M. Eckstein and P. Werner, submitted (2017) [3] D. Golez, P. Werner and M. Eckstein, PRB (2016).

Authors : Keun Su Kim
Affiliations : Department of Physics, Yonsei University, Seoul 03722, Korea

Resume : Two-dimensional (2D) semiconductors have emerged as a class of materials that may impact our future electronics technologies [1]. A key issue is controlling their electronic band structure widely to overcome the limit of natural properties. In this talk, I will introduce our recent angle-resolved photoemission spectroscopy studies on the widely tunable band gap in a 2D semiconductor, black phosphorus. We found that the in situ deposition of alkali-metal atoms modulates the band gap by the giant Stark effect [2,3], resulting in the transition from a trivial narrow-gap semiconductor to a 2D topological Dirac semimetal. After the band inversion, the band topology of semi-metallic black phosphorus can be described by a pair of Dirac cones, similar to that of grapheme [4]. References 1. X. Ling et al., PNAS 112, 4523 (2014). 2. J. Kim et al., Science 349, 723 (2015). 3. M. Kang et al., Nano Lett. 17, 1610 (2017). 4. J. Kim et al., under review (2017).

Authors : Teresa Cusati, Alessandro Fortunelli, Giuseppe Iannaccone
Affiliations : Dipartimento di Ingegneria dell’Informazione, Universita di Pisa, Via G. Caruso 16, 56122 Pisa, Italy; CNR-ICCOM, Istituto di Chimica dei Composti Organometallici, Via G. Moruzzi 1, 56124, Pisa, Italy; Dipartimento di Ingegneria dell’Informazione, Universita di Pisa, Via G. Caruso 16, 56122 Pisa, Italy

Resume : Transition metal dichalcogenides (TMDs), and in particular MoS2, are 2D layered materials whose electronic properties are sensitive to structural changes and interlayer interactions. The number of layers, strain and stacking between layers, the last one induced by weak interlayer van der Waals forces, affect electronic properties and electron transport, and therefore can be tuned in order to optimize their use in electronic devices. Only few studies in the literature focus on the effects of these factors on transport properties. The main aim of our work is to show the effects of the rotation/sliding between layers on the transport properties of multilayer MoS2. We have considered five high-symmetry stacking configurations and performed electronic calculations. Our approach is based on ab initio simulations of structural properties and quantum simulation of electron transport. We have observed different behaviours for the configurations where sulphur atoms sit ‘on top’ with respect to the configurations where they are placed in hollow sites. An improvement in the transmission is shown for some configurations, giving clues about the possible configurations that can be considered in the devices design.

Authors : Daiane Damasceno Borges, Cristiano Woellner, Pedro Autreto, Dougla S. Galvão
Affiliations : Applied Physics Department, University of Campinas - UNICAMP, Campinas-SP 13083-959, Brazil Department of Materials Science and Nano Engineering, Rice University, Houston, Texas, USA; Center for Natural and Human Sciences, Federal University of ABC - UFABC, Santo Andre-SP, 09210-580, Brazil

Resume : Graphene-based nanostructures have been investigated as very promising candidates for water filtration and/or separation membranes. Experimental evidences have shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules [1-2]. The understanding of filtration mechanisms came mostly from studies dedicated to water desalination, while very few works have been dedicated for water distillation. In this work, we have investigated the molecular mechanism underlying the alcohol/water separation inside GO membranes. A series of Molecular Dynamics and Grand-Canonical Monte Carlo simulations were performed to probe the ethanol/water and methanol/water separation through GO membranes composed of multiple layered graphene-based sheets with different interlayer distance and number of functional groups. To rationalize the preferred selectivity of water in nano-confining structure and the effective blocking (rejection) of alcohol molecules, we have carried out detailed atomistic studies. Our results show that both the size exclusion and water molecular arrangement within GO channels are responsible for the separation. The 2D geometry channel is crucial for an effective separation mechanism, since it forces the formation of water monolayers with robust H-bond networks. We conclude that the interlayer separation values and the number of functional groups are key factors for designing more efficient separation membranes. Our results are consistent with the available experimental data and contribute to clarify important aspects of the separation behavior of confined alcohol/water in GO membranes. [1] R. R. Nair et. al. Science 2012, 335 (6067), 442-444 ; [2] R K. Joshi et. al. Science 2014, 343 (6172), 752-754

Authors : Paolo Nicolini, Rosario Capozza, Tomáš Polcar
Affiliations : Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Karlovo náměstí 13, 12135, Prague 2, Czech Republic; Italian Institute of Technology-IIT, via Morego 30, 16163, Genova, Italy; Department of Control Engineering, Faculty of Electrical Engineering, Czech Technical University in Prague, Karlovo náměstí 13, 12135, Prague 2, Czech Republic & Engineering Materials, Faculty of Engineering and Environment, University of Southampton, Southampton SO17 1BJ, United Kingdom

Resume : Molybdenum disulfide, the most studied member of the transition metal dichalcogenides family, has been used as solid lubricant for several decades, showing extremely low friction coefficients[1] and stability to high temperature. Its lubricating properties are ascribed to the weak van der Waals interactions between sulfur atoms in the crystalline layered structure. Moreover MoS2, even when prepared in the amorphous state or made of randomly oriented domains, can undergo shear induced structural transitions to the more ordered layered state affecting its tribological properties[2]. Exploiting a recently developed classical force field[3] able to treat explicitly formation and breaking of bonds, we investigate by molecular dynamics simulations, the shear induced structural changes and possible layer formation in the amorphous molybdenum disulfide. The ordering process is studied in details, with particular regard to the estimation of the thermodynamic properties that govern the process itself. A connection with crystallization theories is finally found, conferring a predictive power to the achieved results. Overall, this study aims at gaining an atomic level understanding of the dynamics of layer formation process in MoS2, thus controlling and possibly improving its tribological properties. [1] J.M. Martin et al., Phys. Rev. B, 48, 10583(R) (1993). [2] J. Moser, F. Lévy, Thin Solid Films, 228, 257 (1993). [3] T. Liang et al., Phys. Rev. B, 79, 245110 (2009).

12:35 Lunch break    
Physical properties and manipulation of 2D materials-I : H. Ding
Authors : Alexei Barinov
Affiliations : Elettra-Sincrotrone Trieste, Trieste, Italy

Resume : I will present novel scanning potoemission microscope capable of acquiring angle resolved photoemission data with sub-micrometer sized beam provided by synchrotron radiation demagnified using multilayer mirrors of a Schwarzschild objectives. This solution provides enough photons for angle resolved photoemission measurements and makes possible investigation of electronic structure of inhomogeneous samples such as superconductors embedded in an insulator as well as artificially prepared heterostructures and devices. Technical solutions and several application examples will be presented.

Authors : Woo Seok Choi
Affiliations : Department of Physics, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Korea

Resume : Combination of functional complex oxides and 2D layered materials let us explore novel physical phenomena and possible device applications in the unprecedented heterostructures. As an example, observation of quantum transport behavior in graphene near the functional transition metal oxides provides new possibilities of understanding the constituent materials. In this presentation, we present examples of synergetic behavior in monolayer graphene on SrTiO3 (STO) epitaxial thin film, using electrical transport measurements. In the first part of the presentation, we show that a large gate-voltage scaling in graphene transport is plausible using STO thin film with the high dielectric constant. The graphene on epitaxial STO thin film shows quantum Hall state which survives up to 200 K at a magnetic field of 14 T. In addition, the substantial shift of charge neutrality point in graphene seems to correlate with the temperature-dependent dielectric constant of the STO thin film, and its effective dielectric properties could be deduced from the universality of quantum phenomena in graphene. [1] In the second part, we show the probing of the creation and annihilation of oxygen vacancies at graphene/STO surface using the quantum conductance of graphene. Since monolayer graphene is highly sensitive to the surrounding electronic environment without modifying it, we can exclusively understand the electronic reconstruction occurring in the STO layer due to oxygen vacancy formation. By analyzing the hysteretic current-voltage loops, we can quantitatively estimate the relation between the thickness, dielectric constant, and oxygen vacancy concentration in oxygen deficient STO layer. [2] [1] J. Park et al., Nano Lett. 16, 1754-1759 (2016). [2] K. T. Kang et al., Adv. Mater. 29, 1700071 (2017).

Authors : Yosuke Goto, Atsuhiro Nishida, Chul-Ho Lee, Yoshikazu Mizuguchi
Affiliations : Yosuke Goto; Atsuhiro Nishida; Yoshikazu Mizuguchi Tokyo Metropolitan University, 1-1, Minami-osawa, Hachioji, Japan Chul-Ho Lee National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1, Umezono, Tsukuba, Ibaraki 305-8568 Japan

Resume : BiS2-based layered compounds, such as LaOBiS2, are an attractive compound that shows unique functionality for superconductivity, thermoelectricity, and so forth. As an example, LaOBiSSe exhibits thermoelectric figure of merit ZT of 0.36 at 650 K (A. Nishida et al. Appl. Phys. Express, 8, 111801 (2015)). This is because of increased carrier mobility and reduced lattice thermal conductivity of LaOBiS2 as a result of Se substitution. In the present study, we report the effect of elemental substitution on thermoelectric properties of LaOBiSSe. So far, Sb, Pb, and Sn have been studied as a dopant. Almost all of doped LaOBiSSe exhibit higher electrical resistivity and Seebeck coefficient than undoped sample, indicating these dopants acted to decrease carrier density. Electrical power factor at moderate temperature (300600 K) can be increased by optimization of amount of substitution. This increased performance is attractive because thermoelectric generator for waste heat harvesting should be operated at a moderate temperature range. In the conference, we will report the further detail of elemental substitution for LaOBiSSe to optimize the thermoelectric performance. Theoretical calculation to discuss the electronic structure will also be presented.

Authors : Manal MYA Alsaif,1 Kourosh Kalantar-zadeh,1 Jian Zhen Ou1
Affiliations : 1 School of Engineering, RMIT University, Australia

Resume : Planar 2D materials are possibly the ideal channel candidates for future field effect transistors (FETs), due to their unique electronic properties. However, the performance of FETs based on 2D materials is yet to exceed those of conventional silicon based devices. Here, a 2D channel thin film made from liquid phase exfoliated molybdenum oxide nanoflake inks with highly controllable substoichiometric levels is presented. The ability to induce oxygen vacancies by solar light irradiation in an aqueous environment allows the tuning of electronic properties in 2D substoichiometric molybdenum oxides (MoO3−x). The highest mobility is found to be ≈ 600 cm2 V−1 s−1 with an estimated free electron concentration of ≈1.6 × 1021 cm−3 and an optimal IOn/IOff ratio of >105 for the FETs made of 2D flakes irradiated for 30 min (x = 0.042). These values are significant and represent a real opportunity to realize the next generation of tunable electronic devices.

15:30 Coffee break    
Physical properties and manipulation of 2D materials-II : A. Barinov
Authors : Volodymyr Khranovskyy1*, Ivan Shtepliuk1, Igor Wlasny2, Piotr Kazmierczak2, and Andrzej Wysmolek2, Zbigniew Klusek3, Kateryna Shavanova4, Yulia Ruban4, Andrii Tencha4 and Rositsa Yakimova1
Affiliations : 1 Department of Physics, Chemistry and Biology (IFM) Linköping University, Linköping, Sweden 2 Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Warsaw, Poland 3 Dept. of Solid State Physics, Faculty of Physics and Applied Informatics, University of Lodz, Poland 4 National University of Life and Environmental Sciences of Ukraine, 03041 Kyiv, Ukraine

Resume : It is now generally accepted that further pro-gress of the semiconductor industry will be governed by achievements in 2D material science in terms of both processing technolo-gies and the incorporation of new materials. Currently there are about 200 companies, involved in the production of graphene – powerfull 2D carbon material of the future. Most of them utilize theliquid chemical exfo-liation processes, which involves use of toxic and dangerous chemicals i. e. hydrazine for reduction purposes. These chemicals can be substituted by non-toxic, environment and human-friendly “green” chemicals, such as ascorbic acid (vitamin C), glucose, caffeic acid or even fruits juice extracts. Their exact influence on the graphene oxide (GO) is not well known yet and deserves detailed study for future application in graphene in-dustrial production. For this purpose, we have studied synthesis of GO by modified Hummers method and its further reduction by various green reagents, engineering its surface (Fig.1). Raman spectra of GO has demonstrated both D and G bands, as well as 2D line, peculiar for 2D carbon materials. The presence of carbonyl (40%), carboxyl (17%), epoxy (3%) and ox-ygen substitution functional groups was iden-tified and quantified on GO surface using XPS spectroscopy (Fig. 2). Upon GO reaction with diverse “green” reductants (Glucose, Vitamin C, Caffeic Acid and Blueberry juice) it was revealed that Vitamin C has the best reducing performance. It turned out, howev-er, that it creates most defects in the reduced rGO material, accordingly to the D/G lines ratio. While Glucose was observed to be the best green reductant in terms of least defects in rGO and best oxygen content decrease performance. Detailed data analysis allows us to claim that glucose as environmentally friendly and non-toxic “green” reductant can be used in the liquid chemical exfoliation processes for graphene production.

Authors : Anna Lapinska [1], Andrzej Taube [1,2], Anna Duzynska [1], Michal Swiniarski [1], Anna Wroblewska [1], Jaroslaw Judek [1] and Mariusz Zdrojek [1].
Affiliations : [1] Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland [2] Also with Institute of Electron Technology, Warsaw, Poland and Institute of Microelectronics and Optoelectronics, Warsaw University of Technology, Warsaw, Poland

Resume : Two dimensional (2D) materials attracts attention of scientific world since the discovery of graphene in 2004. These materials characterise the large variety, one can find such materials as MoS2, WS2, black phosphorus or boron nitride – the best known materials so far. All of 2D materials are unique due to its properties and potential further application as for example photodetectors, solar cells, anode materials for ion-lithium batteries or thermoelectric materials. Despite the fact, the intense works are in progress still a lot of properties of 2D materials are unknown. Here we present the Raman spectroscopy measurements in dependence of temperature which give us better insight to find out thermal properties of layered materials. The knowledge about thermal properties is crucial when operating the electronic devices, especially in terms of the heat conduction and the heat removal due to the power dissipation, which limits electronic devices performance. Herein 2D materials like ReSe2, SnSe2, GeSe, PbSnS2 and black phosphorous were investigated in range of temperature from 70 – 450 K in vacuum conditions. All of these materials shows the non-linear in low temperatures, what is caused by anharmonic phonon decay – three or four phonon decay process. In higher temperature, one can observed the linear behaviour what stays in good agreement with the other known 2D materials. In this range of temperature the first order coefficient were calculated. Finding presented here are important in further analysis of phonon and thermal properties of 2D materials.

Authors : Y. Zhang1, P. De Falco2, Y. Wang2, G. Falkenberg1 and H. S. Gupta2
Affiliations : (1) Photon Science, Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany; (2) Queen Mary University of London, Institute of Bioengineering and School of Engineering and Material Science, London, E1 4NS, UK

Resume : The stomatopod (mantis shrimp) telson serves as an example of natural biological armour whose high impact resistance property is believed to arise from the hierarchical organization of highly mineralised alpha-chitin nanofibres and twisted plywood (Bouligand) structures at the nano and micron scale [1,2]. To determine the structural and mechanical changes of the stomatopod cuticle under external loading can help us to identify the key mechanisms enabling their functional optimization. However, the complex hierarchical structure in biological and synthetic fibrous nanocomposites entails considerable difficulties in the interpretation of the crystallographic texture from diffraction data. Here, we present a novel reconstruction method to image the 3D distribution of fibres from 2D wide-angle X-ray diffraction (WAXD) pattern [3]. Furthermore, we develop a new 3D X-ray nanostrain imaging method combining analytical modelling of the diffraction signal, fibre-composite theory and in situ deformation, to determine the strain and structure change in 3D for different length scale [4]. Our method enables separation of deformation dynamics at multiple hierarchical levels, a critical consideration in the cooperative mechanics characteristic of biological and bioinspired materials. The nanostrain reconstruction technique is general, and can be applied to determine the in situ dynamics of advanced nanostructured materials with 3D hierarchical design.


Symposium organizers
Changyoung KIMSeoul National University

Department of Physics, Seoul 08826, Korea

+82 2 880 6602
Naurang SAINISapienza Università di Roma

Dipartimento di Fisica - P. le Aldo Moro 2 00185 Roma - Italy

+39 0649914387
Sonachalam ARUMUGAMBharathidasan University

Centre for High Pressure Research Palkalaiperur Campus, Tiruchirappalli - 620 024, Tamil Nadu, India

+91 431 2407118
Takashi MIZOKAWAWaseda University

Department of Applied Physics, Waseda University, Tokyo 169-8555, Japan

+81 3 5286 3230