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Topological materials science

Kolloquium der Abteilung 2

Claudia Felser

1Max Planck Institute Chemical Physics of Solids, Dresden, Germany

(e-mail: felser@cpfs.mpg.de)

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 [10-12], Mn3Sn [13-15] and Co3Sn2S2 [16]. 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 [17].

[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]     Shekhar,  et al. arXiv:1703.03736

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

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

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

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

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

[13]   Kübler and Felser, EPL 108 67001 (2014)

[14]   Nayak, et al., Science Advances 2 e1501870 (2016) 

[15]   Nakatsuji, et al., Nature  527 212 (2015) 

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

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