Type-Ii Symmetry-Protected Topological Dirac Semimetals
Tay-Rong Chang1*, Su-Yang Xu2, Daniel S. Sanchez2, Wei-Feng Tsai3, Shin-Ming Huang4, Guoqing Chang3, Chuang-Han Hsu3, Guang Bian2, Ilya Belopolski2, Zhi-Ming Yu5,6, Shengyuan A. Yang6, Titus Neupert7, Horng-Tay Jeng8,9, Hsin Lin3, M. Zahid Hasan2
1Physics, National Cheng Kung University, Tainan, Taiwan
2Physics, Princeton University, New Jersey, USA
3Physics, National University of Singapore, Singapore, Singapore
4Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
5Physics, Beijing Institute of Technology, Beijing, China
68Research Laboratory for Quantum Materials, Singapore University of Technology and Design, Singapore, Singapore
7Physics, University of Zurich, Winterthurerstrasse, Zurich, Swaziland
8Physics, National Tsing Hua University, Hsinchu, Taiwan
9Physics, Academia Sinica, Taipei, Taiwan
* Presenter:Tay-Rong Chang, email:u32trc00@gmail.com
The recent proposal of the type-II Weyl semimetal state has attracted significant interest. In this work, we propose the concept of the three-dimensional type-II Dirac fermion and theoretically identify this new symmetry-protected topological state in the large family of VAl₃ family (VAl₃, NbAl₃, TaAl₃, NbGa₃, and TaGa₃). We show that the VAl₃ family features a pair of strongly Lorentz-violating type-II Dirac nodes and that each Dirac node can be split into four type-II Weyl nodes with chiral charge ±1 via symmetry breaking. Furthermore, we predict that the Landau level spectrum arising from the type-II Dirac fermions in VAl₃ is distinct from that of known Dirac or Weyl semimetals. We also demonstrate a topological phase transition from a type-II Dirac semimetal to a quadratic Weyl semimetal or a topological crystalline insulator via crystalline distortions [1].

[1] T.-R. Chang et al., Phys. Rev. Lett. 119, 026404 (2017)

Keywords: Topological material, Topological semimetal, First-principles calculations, Band theory, spin-orbit coupling