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

Wenhui Wan, Xinyue Liu, Yanfeng Ge, Ziqang Li, Yong Liu

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.

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

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 phase and a metastable T phase, differentiated by iodine atom positions. The T-to-T structural phase transition features a moderate energy barrier 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.
Paper Structure (1 section, 3 equations, 3 figures, 1 table)

This paper contains 1 section, 3 equations, 3 figures, 1 table.

Table of Contents

  1. Data Availability Statement

Figures (3)

  • Figure 1: (a) Surface iodination decomposes the hexagonal lattice of InO ML into two InOI MLs. (b) The energy of InOI ML as a function of Iodine position. The white arrow represents the phase transition path from the T$^{\prime}$ to the T phases. (c) and (d) are the lattice structures of the T and T$^{\prime}$ phases of InOI ML, respectively.
  • Figure 2: (a) The energy profile along the transition path from the T$^{\prime}$ phase to T phase through the diffusion of I atom. (b) The energies of T$^{\prime}$ phase relative to T phase at different biaxial strains. (c) Energy barrier ($E_b$) of T$^{\prime}$-to-T phase transition and that ($E'_b$) of reverse T-to-T$^{\prime}$ phase transition as a function of biaxial strains.
  • Figure 3: (a) The band inversion at the $\Gamma$ point for T-InOI ML. (b) The band structure of T$^{\prime}$-InOI ML. (c) The band gap of T-InOI ML as a function of biaxial strains. The positive and negative band gaps respond to normal insulator (NI) and topological insulator (TI), respectively. (d) Absorption spectra of T and T$^{\prime}$ phases of InOI ML.