Colloquium: Physical properties of group-IV monochalcogenide monolayers

TL;DR

This paper reviews the unique ferroelectric, ferroelastic, optical, and electronic properties of group-IV monochalcogenide monolayers, highlighting their potential in advanced electronic and spintronic applications.

Contribution

It provides a comprehensive survey of the physical properties and potential device applications of these 2D multiferroic materials, emphasizing recent experimental and theoretical insights.

Findings

Display switchable in-plane polarization

Exhibit strong second-harmonic generation and photovoltaic effects

Showcase potential for non-volatile memory and valleytronic devices

Abstract

We survey the state-of-the-art knowledge of ferroelectric and ferroelastic group-IV monochalcogenide monolayers. These semiconductors feature remarkable structural and mechanical properties, such as a switchable in-plane spontaneous polarization, soft elastic constants, structural degeneracies, and thermally-driven two-dimensional structural transformations. Additionally, these 2D materials also display selective valley excitations, valley Hall effects, and persistent spin helix behavior. After a description of their Raman spectra, a discussion of optical properties arising from their lack of centrosymmetry---such as an unusually strong second-harmonic intensity, large bulk photovoltaic effects, photostriction, and tunable exciton binding energies---is provided as well. The physical properties observed in these materials originate from (correlate with) their intrinsic and switchable electric polarization, and the physical behavior hereby reviewed could be of use in non-volatile memory, valleytronic, spintronic, and optoelectronic devices: these 2D multiferroics enrich and diversify the 2D materials toolbox.