Observation of pressure-induced Weyl state and superconductivity in a chirality-neutral Weyl semimetal candidate

Quasiparticle excitations described by the Weyl equation in solids have attracted massive attention in recent years. So far, a wide range of solids which are experimental realized as Weyl semimetals (WSMs) lack for either mirror or inversion symmetry. For the first time, in the absence of both mirror and inversion symmetry, SrSi₂ has been predicted as a robust WSM by recent theoretical works. Here, supported by first-principles calculations, we present systematical angle-resolved photoemission studies of undoped SrSi₂ and Ca-doped SrSi₂ single crystals. Our result shows no evidence of the predicted Weyl fermions at the k_z = 0 plane, as well as the Fermi arcs on (001) surface. With external pressure, the electronic band structure evolves and induces Weyl fermions in this compound, which are revealed by the first-principles calculations combined with electrical transport property measurements. Moreover, superconducting transition is observed with pressure above 20 GPa. Our investigations indicate that SrSi₂ system is good platform to study the topological transition and the correlations with superconductivity.