Topological States in Chevrel Phase Materials from First-principle Calculations

TL;DR

This study uses first-principle calculations to identify nontrivial topological states in Chevrel phase materials, revealing how different metal ions influence their topological and magnetic properties, and suggesting potential for discovering new quantum phenomena.

Contribution

It is the first to identify topological insulator and axion insulator states in Chevrel phase materials through first-principle calculations, highlighting the tunability of topological phases via chemical composition.

Findings

BaMo6S8, SrMo6S8, and Mo6S8 are topological insulators.

EuMo6S8 exhibits axion insulator behavior in ferromagnetic state.

Changing A ions affects topological states and magnetic properties.

Abstract

Chevrel phase materials form a family of ternary molybdenum chalcogenides with a general chemical formula $A_x{\rm Mo}_6X_8$ ($A$ = metal elements, $X$ = chalcogen). The variety of $A$ atoms makes a large number of family members and leads to many tunable physical properties, such as the superconductivity, thermoelectricity and the ionic conductivity. In this work, we have further found various nontrivial band topological states in these materials by using first-principle calculations. The compounds having time-reversal symmetry, such as ${\rm BaMo}_6{\rm S}_8$, ${\rm SrMo}_6{\rm S}_8$, and ${\rm Mo}_6{\rm S}_8$, are topological insulators in both of the $R\bar{3}$ and $P\bar{1}$ phases, whereas ${\rm EuMo}_6{\rm S}_8$ within ferromagnetic state, it is an axion insulator in the $R\bar{3}$ phase and a trivial one in the $P\bar{1}$ phase. This indicates that the change of $A$ ions can modify the chemical potential, lattice distortion, and magnetic orders, which offers a unique way to influence the topological states and other properties. We hope this work can stimulate further studies of Chevrel phase materials to find more intriguing phenomena, such as topological superconducting states and Majorana modes.