Observation of pressure-induced Weyl state and superconductivity in a chirality-neutral Weyl semimetal candidate SrSi2

TL;DR

This study demonstrates pressure-induced Weyl fermions and superconductivity in SrSi2, a candidate Weyl semimetal lacking mirror and inversion symmetry, combining experimental and theoretical approaches to explore topological phase transitions.

Contribution

First experimental observation of pressure-induced Weyl fermions and superconductivity in SrSi2, validating theoretical predictions and expanding understanding of topological phase transitions.

Findings

Weyl fermions induced by pressure in SrSi2

Superconductivity observed above 20 GPa

No Weyl fermions detected at ambient conditions

Abstract

Quasi-particle excitations in solids described by the Weyl equation have attracted significant attention in recent years. Thus far, a wide range of solids that have been experimentally realized as Weyl semimetals (WSMs) lack 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. Herein, supported by first-principles calculations, we present systematic angle-resolved photoemission studies of undoped SrSi2 and Ca-doped SrSi2 single crystals. Our results show no evidence of the predicted Weyl fermions at the kz = 0 plane or the Fermi arcs on the (001) surface. With external pressure, the electronic band structure evolved and induced Weyl fermions in this compound, as revealed by first-principle calculations combined with electrical transport property measurements. Moreover, a superconducting transition was observed at pressures above 20 GPa. Our investigations indicate that the SrSi2 system is a good platform for studying topological transitions and correlations with superconductivity.