Claudia Felser: Joint Quantum Seminar

Prof. Claudia Felser, Max Planck Institute for Chemical Physics of Solids

"Topological materials science"

Topology, a mathematical concept, recently became a hot and truly transdisciplinary topic in condensed matter physics, solid state chemistry and materials science. Since there is a direct connection between real space: atoms, valence electrons, bonds and orbitals, and reciprocal space: bands, Fermi surfaces and Berry curvature, a simple classification of topological materials in a single particle picture should be possible. One important criterion for the identification of the topological material is, in the language of chemistry, the inert pair effect of the s-electrons in heavy elements, and the symmetry of the crystal structure [1]. 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 [2]. Binary phosphides are an ideal material class for a systematic study of Dirac, Weyl and new Fermion physics, since these compounds can be grown as high-quality single crystals. A new class of topological phases that have Weyl points was also predicted in the family that includes NbP, NbAs. TaP, MoP and WP₂. [3-8]. In magnetic materials the Berry curvature and the classical anomalous Hall (AHE) and spin Hall effect (SHE) helps to identify potentially interesting candidates. As a consequence, the magnetic Heusler compounds have already been identified as Weyl semimetals: for example, Co₂YZ [9-11], and Co₃Sn₂S₂[13]. The Anomalous Hall angle also helps to identify materials in which a QAHE should be possible in thin films. Even beyond this reciprocal Berry curvature, Heusler compounds with non-collinear magnetic structures also possess real-space topological states in the form of magnetic antiskyrmions, which have not yet been observed in other materials [13].

[1]   Bradlyn et al., Nature  547  298, (2017)

[2]   Bradlyn, et al., Science 353, aaf5037A (2016).

[3]    Shekhar, et al., Nat. Phys. 11, 645 (2015)

[4]    Liu, et al., Nat. Mat. 15,  27 (2016)

[5]    Yang, et al., Nat. Phys. 11, 728 (2015)

[6]   Gooth et al., Nature 547, 324 (2017)

[7]   Kumar, et al., Nat. Com. 8, 1642  (2017)  

[8]    Gooth et al., Nat. Com 9 (2018) 4093

[9]   Kübler and Felser, EPL 114, 47005 (2016)

[10]  Zhijun Wang, Phys. Rev. Lett. 117, 236401 (2016)

[11]  Chang et al., Scientific Reports 6, 38839 (2016)

[12]  Liu, et al. Nat. Phys. online (2018)

[13]  Nayak, et al., Nature 548, 561 (2017)