Topological phonons in Cs-Te binary systems

Abstract

In this paper, we used symmetry analyses and first-principles calculations to discover seven Cs-Te binary systems that have different crystal structures and can host symmetry-enforced topologically nontrivial phonons: $P{2}_{1}{2}_{1}{2}_{1}\text{\ensuremath{-}}{\mathrm{Cs}}_{2}\mathrm{Te}, Pbam$-CsTe, $Pnma\text{\ensuremath{-}}{\mathrm{Cs}}_{2}\mathrm{Te}, Pm\overline{3}m$-CsTe, $Cmcm\text{\ensuremath{-}}{\mathrm{Cs}}_{2}{\mathrm{Te}}_{5}, Cmc{2}_{1}\text{\ensuremath{-}}{\mathrm{Cs}}_{2}{\mathrm{Te}}_{3}$, and $P{2}_{1}/c\text{\ensuremath{-}}{\mathrm{CsTe}}_{4}$. These phonons include charge-two Dirac point phonons, charge-one Weyl point phonons, quadratic contact triple point phonons, triple point phonons, butterflylike Weyl nodal line phonons, Dirac nodal line phonons, Weyl nodal loop phonons, multiple straight Weyl nodal line phonons, nodal cage phonons, one-nodal surface phonons, two-nodal surface phonons, and three-nodal surface phonons. Furthermore, the relationship between the crystal structure and the topological properties was thoroughly investigated in this study. More importantly, the Cs-Te binary systems clearly exhibit phononic arc-shaped, phononic nodal-line-shaped, phononic drumheadlike, and phononic torus surface states, which benefit experimental detections. Our theoretical results not only propose various experimentally prepared Cs-Te binary systems with exotic topological phonons and phononic surface states but also explain the structure-property relationship for Cs-Te binary systems based on symmetry analyses.