title: New type of Weyl semimetal with quadratic double Weyl fermions.
abstract: Weyl semimetals have attracted worldwide attention due to their wide range of exotic properties predicted in theories. The experimental realization had remained elusive for a long time despite much effort. Very recently, the first Weyl semimetal has been discovered in an inversion-breaking, stoichiometric solid TaAs. So far, the TaAs class remains the only Weyl semimetal available in real materials. To facilitate the transition of Weyl semimetals from the realm of purely theoretical interest to the realm of experimental studies and device applications, it is of crucial importance to identify other robust candidates that are experimentally feasible to be realized. In this paper, we propose such a Weyl semimetal candidate in an inversion-breaking, stoichiometric compound strontium silicide, SrSi2, with many new and novel properties that are distinct from TaAs. We show that SrSi2 is a Weyl semimetal even without spin-orbit coupling and that, after the inclusion of spin-orbit coupling, two Weyl fermions stick together forming an exotic double Weyl fermion with quadratic dispersions and a higher chiral charge of ±2. Moreover, we find that the Weyl nodes with opposite charges are located at different energies due to the absence of mirror symmetry in SrSi2, paving the way for the realization of the chiral magnetic effect. Our systematic results not only identify a much-needed robust Weyl semimetal candidate but also open the door to new topological Weyl physics that is not possible in TaAs.
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546; Department of Physics, National University of Singapore, Singapore 117542;
authors.forename: Shin-Ming
authors.initials: SM
authors.lastname: Huang
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544; suyangxu@princeton.edu nilnish@gmail.com mzhasan@princeton.edu.
authors.forename: Su-Yang
authors.initials: SY
authors.lastname: Xu
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Ilya
authors.initials: I
authors.lastname: Belopolski
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546; Department of Physics, National University of Singapore, Singapore 117542;
authors.forename: Chi-Cheng
authors.initials: CC
authors.lastname: Lee
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546; Department of Physics, National University of Singapore, Singapore 117542;
authors.forename: Guoqing
authors.initials: G
authors.lastname: Chang
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544; Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan; Laboratory for Topological Quantum Matter and Spectroscopy (B7), Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Tay-Rong
authors.initials: TR
authors.lastname: Chang
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546; Department of Physics, National University of Singapore, Singapore 117542; Department of Physics, Northeastern University, Boston, MA 02115;
authors.forename: BaoKai
authors.initials: B
authors.lastname: Wang
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Nasser
authors.initials: N
authors.lastname: Alidoust
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Guang
authors.initials: G
authors.lastname: Bian
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Madhab
authors.initials: M
authors.lastname: Neupane
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Daniel
authors.initials: D
authors.lastname: Sanchez
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544;
authors.forename: Hao
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan; Institute of Physics, Academia Sinica, Taipei 11529, Taiwan;
authors.forename: Horng-Tay
authors.initials: HT
authors.lastname: Jeng
authors.affiliation: Department of Physics, Northeastern University, Boston, MA 02115;
authors.forename: Arun
authors.initials: A
authors.lastname: Bansil
authors.affiliation: Princeton Center for Theoretical Science, Princeton University, Princeton, NJ 08544.
authors.forename: Titus
authors.initials: T
authors.lastname: Neupert
authors.affiliation: Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546; Department of Physics, National University of Singapore, Singapore 117542; suyangxu@princeton.edu nilnish@gmail.com mzhasan@princeton.edu.
authors.forename: Hsin
authors.initials: H
authors.lastname: Lin
authors.affiliation: Joseph Henry Laboratory, Department of Physics, Princeton University, Princeton, NJ 08544; suyangxu@princeton.edu nilnish@gmail.com mzhasan@princeton.edu.
authors.forename: M Zahid
authors.initials: MZ
authors.lastname: Hasan
keywords: Fermi arc; Weyl fermion; chiral magnetic effect; topological insulator