Elasticity of 2D ferroelectrics across their paraelectric phase transformation

TL;DR

This study investigates the finite-temperature elasticity of 2D ferroelectric SnSe monolayers during their phase transition from ferroelectric to paraelectric, revealing how elastic moduli evolve across the transformation.

Contribution

It introduces a comprehensive approach combining elastic energy landscapes and molecular dynamics to analyze 2D phase change elasticity, a novel insight into 2D material behavior.

Findings

Elastic moduli coalesce during phase transition

Elastic parameters exhibit broad evolution and sudden changes

Methodology links 2D materials with soft matter physics

Abstract

The mechanical behavior of two-dimensional (2D) materials across 2D phase changes is unknown, and the finite temperature ($T$) elasticity of paradigmatic SnSe monolayers -- ferroelectric 2D materials turning paraelectric as their unit cell (u.c.) turns from a rectangle onto a square -- is described here in a progressive manner. To begin with, their zero$-T$ {\em elastic energy landscape} gives way to (Boltzmann-like) averages from which the elastic behavior is determined. These estimates are complemented with results from the strain-fluctuation method, which employs the energy landscape or {\em ab initio} molecular dynamics (MD) data. Both approaches capture the coalescence of elastic moduli $\langle C_{11}(T)\rangle=\langle C_{22}(T)\rangle$ due to the structural transformation. The broad evolution and sudden changes of elastic parameters $\langle C_{11}(T)\rangle$, $\langle C_{22}(T)\rangle$, and $\langle C_{12}(T)\rangle$ of these atomically-thin phase-change membranes establishes a heretofore overlooked connection among 2D materials and soft matter.