Tunable double-Weyl Fermion semimetal state in the SrSi₂ materials class

We discuss first-principles topological electronic structure of noncentrosymmetric SrSi₂ materials class based on the hybrid exchange-correlation functional. Topological phase diagram of SrSi₂ is mapped out as a function of the lattice constant with focus on the semimetal order. A tunable double-Weyl Fermion state in Sr_1-xCa_xSi₂ and Sr_1-xBa_xSi₂ alloys is identified. Ca doping in SrSi₂ is shown to yield a double-Weyl semimetal with a large Fermi arc length, while Ba doping leads to a transition from the topological semimetal to a gapped insulator state. Our study indicates that SrSi₂ materials family could provide an interesting platform for accessing the unique topological properties of Weyl semimetals.