Hexagonal InOI monolayer: a 2D phase-change material combining topological insulator states and piezoelectricity

TL;DR

This study predicts a 2D hexagonal InOI monolayer with reversible phase transitions that enable multifunctional electronic, topological, piezoelectric, and optical properties, suitable for advanced device applications.

Contribution

It introduces a novel 2D InOI monolayer with tunable phase transitions and multifunctional properties, expanding the scope of 2D phase-change materials.

Findings

Reversible T' to T phase transition with 72.1 meV barrier.

Strain-induced electronic and topological phase changes.

Modulation of piezoelectricity and optical absorption.

Abstract

Two-dimensional (2D) phase-change materials (PCMs) with moderate transition barriers and distinctly contrasting properties are highly desirable for multifunctional devices, yet such systems remain scarce. Using first-principles calculations, we propose a hexagonal InOI monolayer as a promising 2D PCM. This material exhibits two distinct polymorphs: an energetically favorable T$^{\prime}$ phase and a metastable T phase, differentiated by iodine atom positions. The T$^{\prime}$-to-T structural phase transition features a moderate energy barrier $E_b$ of 72.1 meV per formula unit, facilitating reversible switching. Notably, strain engineering tailors the electronic transition, inducing either a metal-to-topological-insulator or a metal-to-normal-insulator transformation. Additionally, this phase transition modulates the piezoelectric response and shifts optical absorption from the infrared to the visible range. These multifunctional properties make 2D hexagonal InOI highly promising for applications in non-volatile memory, low-contact-resistance spintronics, and optical switching devices.