Non-monotonic thickness dependence of Curie temperature and ferroelectricity in Two-dimensional SnTe film

TL;DR

This study uses density functional theory to explore how the Curie temperature and ferroelectricity in 2D SnTe vary with thickness, revealing a non-monotonic relationship with a maximum at 8 layers and tunability via strain.

Contribution

It uncovers the non-monotonous thickness dependence of Curie temperature in 2D SnTe and explains the underlying surface effects and atomic distortions.

Findings

Curie temperature peaks at 8 atomic layers.

Surface effects induce periodic bilayer structure.

External strain can tune the Curie temperature.

Abstract

Recently, the observation of atomic thin film SnTe with a Curie temperature (Tc) higher than that of the bulk (Chang et. al., Science 353, 274 (2016)) has boosted the research on two-dimensional (2D) ferroic materials tremendously. However, the origin of such phenomenon has yet been thoroughly investigated, which hinder the understanding and design of novel materials with ferroic orders at 2D limit. By using the density functional theory, we investigated the structural and ferroelectrical properties of 2D SnTe, to reveal the thickness dependence. The calculated results demonstrate that the 2D SnTe automatically transform into periodical bilayer structure, resulting from the surface effect. Moreover, based on the double-well potential and atomic distortion analysis, we found the Tc of the 2D SnTe is higher than the bulk counterpart, and more surprisingly, the Tc exhibits an unusual non-monotonous dependence of thickness, featuring a pronounced atomic distortion and Curie temperature maximum at 8 atomic-layers. In addition, this non-monotonous dependence is sensitive to the external strain and it can be tuned easily by the external compressive strain.