Large Fermi-arc and robust Weyl semimetal phase in Ag$_2$S

TL;DR

This paper predicts that Ag$_2$S is a robust Weyl semimetal with long Fermi-arcs, based on first-principles calculations, showing stability against strain and potential for topological applications.

Contribution

It identifies Ag$_2$S as a topological Weyl semimetal with robust Weyl points and long Fermi-arcs, expanding the class of materials with topological semimetal phases.

Findings

Ag$_2$S is a topological Dirac semimetal without SOC.

SOC splits Dirac points into Weyl points with opposite chirality.

Weyl points are far apart, making them robust and leading to long Fermi-arcs.

Abstract

Three-dimensional Dirac and Weyl semimetals have attracted widespread interest in condensed matter physics and material science. Here, based on first-principles calculations and symmetry analysis, we report that Ag$_2$S with P2$_1$2$_1$2$_1$ symmetry is a topological Dirac semimetal in the absence of spin-orbit coupling (SOC). Every Dirac points are composed of two Weyl points with the same chirality overlapping in the momentum space. After taking the SOC into consideration, each Dirac point is split into two Weyl points. The Weyl points with the opposite chirality are far from each other in the momentum space. Therefore, the Weyl pairs are not easy to annihilate and robust in the Ag$_2$S compound, which also lead to long Fermi-arcs on material surface. The robustness of the Weyl points against the strain is discussed.