IMX Seminar Series - Topology and Chirality

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. Beyond Weyl and Dirac, new fermions can be identified in compounds that have linear and quadratic 3-, 6- and 8- band crossings that are stabilized by space group symmetries. Crystals of chiral topological materials CoSi, AlPt and RhSi were investigated by angle resolved photoemission and show giant unusual helicoid Fermi arcs with topological charges (Chern numbers) of ±2. In agreement with the chiral crystal structure two different chiral surface states are observed. A quantized circular photogalvanic effect is theoretically possible in Weyl semimetals. However, in the multifold fermions with opposite chiralities where Weyl points can stay at different energies, a net topological charge can be generated.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 Observation and control of maximal Chern numbers in a chiral topological semimetal, Niels B.M. Schröter, Samuel Stolz, Kaustuv Manna, Fernando de Juan, Maia G. Vergniory, Jonas A. Krieger, Ding Pei, Pavel Dudin, Timur K. Kim, Cephise Cacho, Barry Bradlyn, Horst Borrmann, Marcus Schmidt, Roland Widmer, Vladimir Strokov, and Claudia Felser, Science 369 (2020) 179
2 Evidence for an axionic charge density wave in the Weyl semimetal (TaSe4)2I, Johannes Gooth, Barry Bradlyn, Shashank Honnali, Clemens Schindler, Nitesh Kumar, Jonathan Noky, Yangpeng Qi, Chandra Shekhar, Yan Sun, Zhijun Wang, Bogdan Andrei Bernevig, Claudia Felser, Nature 575 (2019) 315–319

Bio: Claudia Felser studied chemistry and physics at the University of Cologne, completing there both her diploma in solid state chemistry (1989) and her doctorate in physical chemistry (1994). After postdoctoral fellowships at the Max Planck Institute in Stuttgart (Germany) and the CNRS in Nantes (France), she joined the University of Mainz in 1996 as an assistant professor (C1) becoming a full professor there in 2003 (C4). She is currently Director at the Max Planck Institute for Chemical Physics of Solids in Dresden. In 2001 Felser received Order of Merit (Landesverdienstorden) of the state Rheinland Pfalz for the foundation of the first NAT-LAB for school students at the University Mainz with a focus in female school students. She is fellow of the IEEE Magnetic Society, American Physical Society, Institute of Physics, London, CIFAR Canada and the Materials Research Society of India. In 2018, she became a member of the Leopoldina, the German National Academy of Sciences, and acatech, the German National Academy of Science and Engineering. In 2011 and again in 2017, she received an ERC Advanced grant. In 2019, Claudia Felser was awarded the APS James C. McGroddy Prize for New Materials together with Bernevig (Princeton) and Dai (Hongkong). In 2020, she was elected to the United States National Academy of Engineering (NAE) and in 2021 to the United States National Academy of Sciences (NAS). In 2022 she was awarded the Max Born Prize and Medal of DPG and IOP, the Liebig Medal of the Gesellschaft Deutscher Chemiker (GDCh) and the Wilhelm-Ostwald-Medal of the Saxon Academy of Science. Her research foci are the design, synthesis, and physical characterization of new quantum materials, in particular, Heusler compounds and topological materials for energy conversion and spintronics.