Double Weyl fermions of quadratic-dispersion in mirror-symmetry-free SrSi₂
Shin-Ming Huang1,2*, Su-Yang Xu3, Ilya Belopolski3, Chi-Cheng Lee1,2, Guoqing Chang1,2, Tay-Rong Chang4,3, BaoKai Wang1,2,5, Nasser Alidoust3, Guang Bian3, Madhab Neupane3, Daniel Sanchez3, Hao Zheng3, Horng-Tay Jeng4,6, Arun Bansil5, Titus Neupert7, Hsin Lin1,2, M. Zahid Hasan4
1Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, Singapore
2Department of Physics, National University of Singapore, Singapore, Singapore
3Department of Physics, Princeton University, Princeton, New Jersey, USA
4Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
5Department of Physics, Northeastern University, Boston, Massachusetts, USA
6Institute of Physics, Academia Sinica, Academia Sinica, Taiwan
7Princeton Center for Theoretical Science, Princeton University, Princeton, New Jersey, USA
* presenting author:Shin-Ming Huang,
The pursuit of time-reversal-symmetric Weyl semimetals (WSMs) is just at the startup stage. To realize such systems, breaking of inversion symmetry is required. In 2015, we had succeeded in finding WSMs in TaAs class. In this talk, I will present our another theoretical proposal of WSM candidate—SrSi₂. According to first-principles calculations, SrSi₂ is a WSM regardless of spin-orbit coupling and the Weyl fermions turn into ones with higher chiral charge of 2 in the presence of the spin-orbit coupling. These Weyl fermions are protected by rotation symmetry and show quadratic dispersion perpendicular to rotation axes. Moreover, we find that the Weyl fermions with opposite charges are located at different energies due to the absence of mirror symmetry in SrSi₂, indicating a novel topological quantum response that an external magnetic field can induce a dissipationless current.

Keywords: Weyl semimetals, inversion symmetry breaking, chiral magnetic effect