# Pressure-controlled Structural Symmetry Transition in Layered InSe

## TL;DR

This paper demonstrates a reversible, pressure-controlled transition in the structural symmetry of layered InSe, monitored via SHG spectroscopy, revealing new ways to manipulate 2D material properties.

## Contribution

It introduces a novel method to reconfigure the symmetry of layered InSe using pressure, enabling in-situ control of crystal symmetry in 2D materials.

## Key findings

- Reversible symmetry transition observed from three-fold to mirror symmetry.
- Pressure induces continuous evolution of structural symmetries.
- Interlayer-translation model explains the symmetry change.

## Abstract

Structural symmetry of crystals plays important roles in physical properties of two-dimensional (2D) materials, particularly in the nonlinear optics regime. It has been a long-term exploration on the physical properties in 2D materials with various stacking structures, which correspond to different structural symmetries. Usually, the manipulation of rotational alignment between layers in 2D heterostructures has been realized at the synthetic stage through artificial stacking like assembling Lego bricks. However, the reconfigurable control of translational symmetry of crystalline structure is still challenging. High pressure, as a powerful external control knob, provides a very promising route to circumvent this constraint. Here, we experimentally demonstrate a pressure-controlled symmetry transition in layered InSe. The continuous and reversible evolution of structural symmetries can be in-situ monitored by using the polarization-resolved second harmonic generation (SHG) spectroscopy. As pressure changes, the reconfigurable symmetry transition of the SHG pattern from three-fold rotational symmetry to mirror symmetry was experimentally observed in a layered InSe samples and was successfully explained by the proposed interlayer-translation model. This opens new routes towards potential applications of manipulating crystal symmetry of 2D materials.

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Source: https://tomesphere.com/paper/1903.04315