Interface engineering of ferroelectricity in thin films of thiophosphate ABP 2 X 6 (A = Cu, Ag; B = In, Bi, Cr, V; and X = S, Se)

Guoliang Yu; Anlian Pan; Mingxing Chen

doi:10.1103/PhysRevB.104.224102

paper

Interface engineering of ferroelectricity in thin films of thiophosphate ABP 2 X 6 (A = Cu, Ag; B = In, Bi, Cr, V; and X = S, Se)

arXiv:2112.04077 · doi:10.1103/PhysRevB.104.224102

Abstract

Two-dimensional ferroelectrics (FEs) are promising in the miniaturization of memory devices with ultra-high-density data storage and low power consumption. However, many thiophosphate monolayers, i.e., analogs of CuInP $_{2}$ S $_{6}$ and referred to as ABP $_{2}$ X $_{6}$ , lose ferroelectricity and instead exhibit an antiferroelectric (AFE) or paraelectric ordering. We propose to tune the AFE ABP $_{2}$ X $_{6}$ monolayers into the FE ordering through interface engineering. The mechanism is that there are couplings between the charge polarizations of the ABP $_{2}$ X $_{6}$ monolayers and the local dipoles as well as the induced electronic polarizations in the substrate which have a tendency to stabilize the FE ordering. We further perform first-principles calculations for CuInP $_{2}$ Se $_{6}$ and CuCrP $_{2}$ S $_{6}$ monolayers and their van der Waals heterostructures. We find that an AFE CuInP $_{2}$ Se $_{6}$ monolayer becomes FE as interfaced with graphene, MoS $_{2}$ , and h-BN monolayers. In contrast, the CuCrP $_{2}$ S $_{6}$ monolayer remains AFE since there is a large energy difference between the AFE and FE phases. Interfacing it with a MoTe $_{2}$ monolayer induces a metal-insulator transition for the heterostructure, whereas interfacing with a polar surface MgO(111) can drive it into FE. The interfacing effect can also be used to manipulate the FE properties of ABP $_{2}$ X $_{6}$ multilayers. We further find that the AFE-to-FE transition is electrically switchable in these systems. In particular, it is accompanied by an indirect-direct band-gap transition for the CuInP $_{2}$ Se $_{6}$ monolayer. Our study offers an effective approach to tune the FE and electronic properties of ABP $_{2}$ X $_{6}$ thin films for applications in electronics and optoelectronics.

10 pages, 16 figures

Interface engineering of ferroelectricity in thin films of thiophosphate ABP 2 X 6 (A = Cu, Ag; B = In, Bi, Cr, V; and X = S, Se)

Abstract

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