Octuple-state sliding ladder ferroelectrics in bilayer van der Waals GeSe/SnS heterostructures

Advancing next-generation high-density data storage and post-Moore computing technologies requires the engineering of higher-order multistate ferroelectric transitions. In this study, we demonstrate an octuple-state sliding ladder ferroelectric behaviour in bilayer GeSe/SnS van der Waals heterostructures. This behaviour arises from compression-modulated interlayer sliding, which induces a series of multi-step phase transitions. Enhanced interlayer coupling enables the emergence of two novel intermediate phases, in addition to the conventional ferroelectric and ferrielectric states, resulting in an unprecedented eight-state ferroelectric system. Energy decomposition analysis reveals that the stability of these phases is governed by the interplay between compression-tuned interlayer interactions and intralayer mechanical deformation. Notably, bilayer GeSe/SnS exhibits a closed-loop ferroelectric transition pathway, allowing reversible cycling through all eight polarization states solely via interlayer sliding. This loop forms a ladder-like sequence of discrete polarization states, laying a foundation for the development of multistate ferroelectric systems that surpass traditional binary architectures. These findings provide new insights into the fundamental mechanisms of phase transitions and polarization switching in two-dimensional van der Waals heterostructures.