Structural phase transition in monolayer gold(I) telluride: From a room-temperature topologicalinsulator to an auxetic semiconductor

TL;DR

This study reveals a reversible structural phase transition in monolayer gold(I) telluride, transforming it from a topological insulator to an auxetic semiconductor under strain, with implications for phase-change nanoelectronics.

Contribution

It identifies two stable 2D phases of Au₂Te with distinct electronic properties and elucidates the phase transition mechanism using computational methods.

Findings

s(II)-Au₂Te is a room-temperature topological insulator

s(I)-Au₂Te is an auxetic semiconductor with high mobility

Phase transition can be induced by small tensile strain

Abstract

Structural phase transitions between semiconductors and topological insulators have rich applications in nanoelectronics but are rarely found in two-dimensional (2D) materials. In this work, by combining ab initio computations and evolutionary structure search, we investigate two stable 2D forms of gold(I) telluride (Au$_{2}$Te) with square symmetry, noted as s(I)- and s(II)-Au$_{2}$Te. s(II)-Au$_{2}$Te is the global minimum structure and is a room-temperature topological insulator. s(I)-Au$_{2}$Te is a direct-gap semiconductor with high carrier mobilities and unusual in-plane negative Poisson's ratio. Both s(I) and s(II) phases have ultra-low Young's modulus, implying high flexibility. By applying a small tensile strain, s(II)-Au$_{2}$Te can be transformed into s(I)-Au$_{2}$Te. Hence, a structural phase transition from a room-temperature topological insulator to an auxetic semiconductor is found in the 2D forms of Au$_{2}$Te, which enables potential applications in phase-change electronic devices. Moreover, we elucidate the mechanism of the phase transition with the help of phonon spectra and group theory analysis.