Three-dimensional topological Dirac materials

DIPC Seminars

Dr. Andreas Schnyder, Max Planck Institute for Solid State Research
Donostia International Physics Center
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Three-dimensional topological Dirac materials Although topologically nontrivial properties are normally associated with insulating phases, recent developments have shown that (semi)metallic phases can also be topological. In this talk, I will survey recent developments regarding the topological classifications of (semi)metallic materials in terms of crystal symmetries [1,2]. As a concrete examples, I will present results about the recently discovered compound Ca3P2 [3], which has a line of Dirac nodes near the Fermi energy. I will discuss the topological properties of Ca3P2 in terms of a low-energy effective theory and a tight-binding model, derived from ab-initio DFT calculations. The microscopic model for Ca3P2 shows that the drumhead surface states have a rather weak dispersion, which implies that correlation effects are enhanced at the surface of Ca3P2. Furthermore, I will discuss the parity anomaly that exists in this nodal-line semimetal and show how it is connected to unusual transport phenomena. As a second example, I will survey the topological properties of the Dirac materials A3EO [4], where A denotes an alkaline earth metal, while E stands for Pb or Sn. I will discuss the magnetic properties of this Dirac system and show that a strong Zeeman field splits the gapped Dirac cones into ungapped Weyl points, which are protected by a quantized Chern number. If time permits, I will also present some results about non-centrosymmetric superconductors and their Majorana flat-band surface states. [1] Ching-Kai Chiu, Andreas P. Schnyder, Phys. Rev. B 90, 205136 (2014). [2] Y. X. Zhao, Andreas P. Schnyder, Z. D. Wang, Phys. Rev. Lett. 116, 156402 (2016). [3] Y.-H. Chan, Ching-Kai Chiu, M. Y. Chou, A. P. Schnyder, Phys. Rev. B 93, 205132 (2016). [4] Ching-Kai Chiu, Y.-H. Chan, Xiao Li, Y. Nohara, A. P. Schnyder , arXiv:1606.03456 (submitted).