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

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 (Au2Te) with square symmetry, noted as s(I)- and s(II)-Au2Te. s(II)-Au2Te is the global minimum structure and is a room-temperature topological insulator. s(I)-Au2Te 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 ultralow Young's modulus, implying high flexibility. By applying a small tensile strain, s(II)-Au2Te can be transformed into s(I)-Au2Te. Hence, a structural phase transition from a room-temperature topological insulator to an auxetic semiconductor is found in the 2D forms of Au2Te, 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.