Interfacial ferroelectricity at naturally-formed van der Waals interfaces

Sliding ferroelectrics emerge as compelling candidates for next-generation wafer-level non-volatile storage applications with low power consumption and high packing density. However, artificially stacked sliding ferroelectrics with homogeneous/heterogeneous interfaces rely on highly complex procedures that offer only limited scalability and reproducibility, while van der Waals layered materials that naturally exhibit vertical spontaneous polarization and experimentally confirmed sliding ferroelectricity remain limited. Here, we report interlayer directional sliding-induced interfacial ferroelectricity in van der Waals layered SnSe₂ semiconductors with different naturally-formed stacking configurations. Comprehensive piezoresponse force microscopy measurements confirm the robust and non-volatile out-of-plane ferroelectricity in SnSe₂ flakes with non-centrosymmetric interfaces. In-situ biasing scanning transmission electron microscopy investigations simultaneously visualize the external field induced interfacial sliding and the coupled reversible polarization switching. Theoretical calculations consistently support the sliding paths in non-centrosymmetric SnSe₂. Our results could indicate universal out-of-plane ferroelectricity in van der Waals layered materials with non-centrosymmetric interfaces and extend the family of ferroelectric semiconductors like SnSe₂, which have potential for large-scale integrated applications in ferroelectric photovoltaics, ferroelectric tunnel junctions and in-memory computing.