Ferroelectricity in 2D crystals of CuInP₂S₆ and other transition metal chalcogenides

Ferroelectricity in 2D crystals has attracted a great deal of interest recently because of its fundamental physics and potential applications. Semiconducting CuInP₂S₆ (CIPS), the only van der Waals (vdW) layered material whose ferroelectricity in the bulk was demonstrated by direct polarization measurements, was shown to remain ferroelectric down to a thickness of a few nanometers. Ferroelectricity has also been reported in 2D crystals of other transition metal chalcogenides, including those prepared through stacking engineering. Metal-ferroelectric semiconductor-metal trilayer structures were found to be an effective platform to explore properties of 2D crystal ferroelectrics. We prepared trilayer structures featuring mechanical exfoliated flakes of CIPS different material combinations and the measurements of current-voltage characteristics and observed rectifying behavior and four bias voltage and polarization dependent resistive states, which can be attributed to the formation of Schottky barrier that is modulated by the switching of electric polarization in CIPS. Other observations will also be reported.