Plenary session

Topology and chirality

Claudia Felser
Max Planck Institute Chemical Physics of Solids, Dresden, Germany

Topology, a well-established concept in mathematics, has nowadays become essential to describe condensed matter. At its core are chiral electron states on the bulk, surfaces and edges of the condensed matter systems, in which spin and momentum of the electrons are locked parallel or anti-parallel to each other. Magnetic and non-magnetic Weyl semimetals, for example, exhibit chiral bulk states that have enabled the realization of predictions from high energy and astrophysics involving the chiral quantum number, such as the chiral anomaly, the mixed axial-gravitational anomaly and axions. The potential for connecting chirality as a quantum number to other chiral phenomena across different areas of science, including the asymmetry of matter and antimatter and the homochirality of life, brings topological materials to the fore.

1. Topological Quantum Chemistry: Bradlyn et al., Nature  547  298, (2017), Vergniory, et al., Nature 566 480 (2019), Xu et al. Nature 586 (2020) 702,
2. New Femions: Bradlyn, et al., Science 353, aaf5037A (2016), Sanchez et al., Nature 567 (2019) 500, Schröter et al., Nature Physics 15 (2019) 759, Schröter Science 369 (2020) 179, Sessi et al, Nature Communications 11 (2020) 3507, Yao et al., Nature Communications 11 (2020) 2033, Y. Yen, et al., Nat.  Physics 2024 online preprint arXiv:2311.13217
3. Catalysis: B. Yan, et al., Nature Com. 6 (2015) 10167, Guowei Li and Claudia Felser, APL 116 (2020) 070501. Qun Yang, et al., Advanced Materials 32 (2020) 1908518, G Li, et al., Angewandte Chemie 135 (2023), e202303296

Chiral electron with spin momentum locked and chiral molecules and their mirror image

The role of material science in power electronics

S. Coffa
Robert Bosch GmbH, Reutlingen ­- Mobility Electronics Department, Power Semiconductors and Modules

In this talk the importance of new materials introduction in semiconductor processing is highlighted. In particular, cases in which materials science innovation have been combined with proper industrial exploration of the new materials properties will be discussed. As known, performances of power devices are of paramount importance in energy consumption reduction in many practical applications.  The roadmaps of modern power devices is driven by three major development pillars; a) novel elementary cell structure; b) advanced interconnects; c) use of different semiconductor materials (moving from Si to  SiC and GaN). Improvements in any of these pillars are strongly driven by new materials introduction. The focus of the presentation is to show how the introduction of  SiC and GaN with their superior electronic and thermal properties (and in spite of problems linked to defects and higher costs compared to Si) has revolutionized the field of power devices. Today semiconductor companies are heavily using SiC and GaN in the production of power devices. This has been made possible by the huge work of the material science community (improvement in crystal growth, epitaxy, defect reduction and screening, use of ion implantation on compound semiconductor, etc). Finally, it will be shown that the lower defect density, the larger availability, the possibility to use large area substrates and the overall reduction in costs achieved for SiC, is offering the possibility to use the material for other applications (SiC integrated photonics, quantum computing and others still to come)

Imaging the properties of atoms and fields down to the
picometer scale inside materials and devices

David A Muller
School of Applied Physics, Cornell University, USA

With recent advances in detector technology and ptychographic phase-retrieval algorithms to unscramble multiple scattering, the resolution of the electron microscope is now limited only by the dose applied to the sample, and thermal vibrations of the atoms themselves.  At high doses, these approaches have allowed us to image the detailed vibrational envelopes of individual atom columns as well as locating individual interstitial atoms.  The three-dimensional nature of the reconstruction means surface relaxations can be distinguished from the bulk structure, and atomic-scale interface roughness and step edges inside devices can be resolved – including gate-all-around transistors and Josephson junctions. Even the location of all atoms in thin amorphous films now seems within reach. The reduced sensitivity to chromatic aberrations also makes these ptychographic-like approaches of interest for thick biological or polymer samples or operando liquid-cell experiments, where we have been able to demonstrate a fivefold improvement in dose efficiency over conventional cryo-EM.