Researchers proposed a new concept for transient negative capacitance (NC) based on inverse polarization switching against the electric field in layered van der Waals (vdW) ferrielectric CuInP2S6. This innovation offers a pathway towards new designs for efficient computing based on intrinsic material properties without the need for additional circuitry.
In CuInP2S6, which has a layered crystallographic structure with high Cu-ion mobility, the Cu position determines the ferrielectric polarization. When the polarization of the electric field is reversed, Cu migrates across the vdW gap. Density functional theory calculations show that this process results in polarization alignment against the electric field; this alignment is opposite to the one found in regular ferroelectric materials. Piezoresponse force microscopy revealed that it is possible to isolate the Cu transition across the vdW gaps reversibly on local scales, resulting in inverse polarization loops that exhibit two negative slopes constituting NC regimes. This interplay of ionic and polar properties enables stable NC during polarization switching, unlike transient NC methods based on ferroelectric circuits.
