Evidence of phase stability, topological phonon and temperature-induced topological phase transition in rocksalt SnS and SnSe

TL;DR

This study investigates the phase stability, topological phonons, and temperature-induced topological phase transitions in rocksalt SnS and SnSe, revealing their potential for device applications due to their thermally tunable topological properties.

Contribution

It predicts phase stability of SnS considering Sn 4p orbitals and demonstrates temperature-induced topological phase transitions in SnS and SnSe.

Findings

SnS is phase stable in rocksalt structure with detailed phonon analysis.

Topological phonons are observed along the X-W direction.

Topological phase transition occurs around 700 K due to electron-phonon interaction.

Abstract

Both SnS and SnSe have been experimentally and theoretically confirmed as topological crystalline insulators in native rocksalt structure. Here, phononic structure, thermodynamical properties and temperature dependent electron-phonon interaction (EPI) have investigated for both the materials in rocksalt phase. Previously performed theoretical studies have predicted the phase instability of SnS in this crystal structure at ambient condition. But, after a detailed study performing on the phonon calculation of SnS, we have predicted the phase stability of SnS with considering the Sn 4$p$ orbitals as valence states in $ab-initio$ calculation. The importance of long range Coulomb forces along with the themodynamical properties are also described in detailed for both materials. The preliminary evidence of topological phonon is found along X-W direction, where the linear band touching is observed as compared to type II Weyl phononic material ZnSe. The topological phase transition is seen for these materials due to EPI, where non-linear temperature dependent bandgap is estimated. The predicted value of transition temperature for SnS (SnSe) is found to be $\sim$700 K, where after this temperature the non-trivial to trivial topological phase is seen. The strength of EPI shows more stronger impact on the electronic structure of SnS than SnSe material. The reason of non-linear behaviour of bandgap with rise in temperature is discussed with the help of temperature dependent linewidths and lineshifts of conduction band and valence band due to EPI. The present study reveals the phase stability of SnS along with the comparative study of thermal effect on EPI of SnS and SnSe. Further, the possibility of temperature induced topological phase transition provides one of important behaviour to apply these two materials for device making application.