First-principles evidence of type-II Weyl phonons in rock-salt Tin Chalcogenides (SnS, SnSe & SnTe) materials

TL;DR

This study uses first-principles calculations to demonstrate that rock-salt SnS, SnSe, and SnTe exhibit type-II Weyl phonons with topological surface states and Fermi arcs, advancing understanding of topological phononic materials.

Contribution

It provides the first evidence of type-II Weyl phonons in rock-salt SnS, SnSe, and SnTe using ab initio methods, revealing their topological phononic properties.

Findings

Weyl points identified at specific frequencies for each material

Surface arcs observed in surface local density of states

Presence of topological phononic surface states confirmed

Abstract

Recent studies on different topological materials in condensed matter physics have provided the evidence of topological nature for bosonic particle like phonons by performing various theoretical calculations and experimental observations. Here, the topological behaviours of phonons of SnS, SnSe and SnTe materials in rock-salt structure are investigated using $ab$-$initio$ methodology. For all these materials, the tilted linear band touching is observed along with the presence of band inversion in direction X-W. The topological point in phonon dispersion curve along X-W direction is found to be $\sim$2.83, $\sim$2.46 and $\sim$2.51 THz for SnS, SnSe and SnTe, respectively. The calculated numbers of Weyl points (WPs) is estimated to be 56, 24 and 54 for SnS, SnSe and SnTe, respectively. These WPs have shown conserved Chiral charges for all corresponding materials. The surface local density of states is computed for these compounds, where the surface arc is clearly seen. In case of SnS, the surface arc is found at 2.0 - 2.2 THz energy region. Also, the isofrequency surface states are investigated to observe the presence of Fermi arc for SnX (X = S, Se, Te). The present first-principles calculation predicts that SnS, SnSe and SnTe show type-II Weyl phononic behaviour along with evidence of topological phononic surface states.