Multistate Polarization and Enhanced Nonreciprocal Transport in Two-Dimensional van der Waals Ferroelectric Heterostructures

Achieving multiple switchable polarization states at the nanoscale is crucial to high-density nonvolatile multistate memory beyond bistable ferroelectric architectures. Here, we propose a novel strategy to realize multistate polarization and enhance nonreciprocal transport in two-dimensional (2D) van der Waals ferroelectric heterostructures. By integrating two distinct 2D ferroelectric materials with substantial spontaneous polarizations, we demonstrate that the Bi/SnTe heterostructure can support up to eight distinct polarization states. Our first-principles analysis of transforming paths and corresponding energy barriers reveals that these states can be mutually switched by applying external electric fields, facilitated by a combination of intralayer polar distortion and interlayer sliding. Moreover, the Bi/SnTe heterostructure exhibits significantly enhanced nonlinear Hall and kinetic magnetoelectric effects, closely correlated to the multistate in-plane and persistent out-of-plane polarization. These findings open new possibilities for designing advanced ferroelectric devices with multiple polarization states and enhanced nonreciprocal transport, offering a pathway toward next-generation memory and nanoelectronics.