Topological states and topological phase transition in Cu2SnS3 and Cu2SnSe3

TL;DR

This paper uses first-principles calculations to show how Cu2SnS3 and Cu2SnSe3 transition between different topological states, including nodal line semimetals, Weyl semimetals, and topological insulators, driven by spin-orbit coupling.

Contribution

It reveals a tunable topological phase transition in Cu2SnS3 and Cu2SnSe3, demonstrating control over Weyl nodes and topological states through spin-orbit coupling effects.

Findings

Cu2SnS3 is a nodal line semimetal without SOC.

SOC induces Cu2SnS3 into a Weyl semimetal state.

SOC transforms Cu2SnSe3 into a strong topological insulator.

Abstract

Based on the first-principles calculations within local density approximation and model analysis, we propose that the iso-structural compounds Cu2SnS3 and Cu2SnSe3 are both the simplest nodal line semimetals with only one nodal line in their crystal momentum space when spin-orbit coupling (SOC) is ignored. The including of SOC drives Cu2SnS3 into a Weyl semimetal (WSM) state with only two pairs of Weyl nodes, the minimum number required for WSM with time reversal symmetry. In contrast, SOC leads Cu2SnSe3 to strong topological insulator (TI) state. This difference can be well understood as there is a topological phase transition (TPT). In it, the Weyl nodes are driven by tunable SOC and annihilate in a mirror plane, resulting in a TI. This TPT, together with the evolution of Weyl nodes, the changing of mirror Chern numbers of mirror plane and the Z2 indices protected by time-reversal symmetry has been demonstrated by the calculation of Cu2SnS3-xSex within virtual crystal approximation and an effective k $\cdot$ p model analysis. Though our first-principles calculations have overestimated the topological states in both compounds, we believe that the theoretical demonstration of controlling TPT and evolution of Weyl nodes will stimulate further efforts in exploring them.