Robust Ferroelectricity in Monolayer Group-IV Monochalcogenides

TL;DR

This paper demonstrates that monolayer group-IV monochalcogenides exhibit robust in-plane ferroelectricity due to ionic anharmonicity, with a Curie temperature above room temperature, promising for ultra-thin ferroelectric devices.

Contribution

It reveals that ionic-potential anharmonicity induces stable in-plane ferroelectricity in monolayer group-IV monochalcogenides, supported by first-principles calculations and Monte Carlo simulations.

Findings

Ferroelectricity persists in monolayer form due to ionic anharmonicity.

The materials exhibit a two-dimensional ferroelectric phase transition.

Curie temperature exceeds room temperature, indicating practical applicability.

Abstract

Ferroelectricity usually fades away when materials are thinned down below a critical value. Employing the first-principles density functional theory and modern theory of polarization, we show that the unique ionic-potential anharmonicity can induce spontaneous in-plane electrical polarizations and ferroelectricity in monolayer group-IV monochalcogenides MX (M=Ge, Sn; X=S, Se). Using Monte Carlo simulations with an effective Hamiltonian extracted from the parameterized energy space, we show these materials exhibit a two-dimensional ferroelectric phase transition that is described by fourth-order Landau theory. We also show the ferroelectricity in these materials is robust and the corresponding Curie temperature is higher than room temperature, making these materials promising for realizing ultra-thin ferroelectric devices of broad interest.