Resolving polarization switching pathways of sliding ferroelectricity in trilayer 3R-MoS2

Abstract

Sliding ferroelectricity, an emerging type of hysteretic behaviour with strong potential for memory-related applications, involves dynamically switching the polarization associated with the stacking arrangement in two-dimensional van der Waals materials. Because different stacking configurations can share a degenerate net polarization, it has remained a challenge to resolve the intermediate stacking configuration and the polarization switching pathway in multi-interface devices. In this work, we present an optical approach to resolve the polarization degeneracy in a trilayer 3R-MoS2 over different switching cycles. By performing reflection contrast spectroscopy in dual-gated devices, we identify distinct responses of inter- and intralayer excitons in all four possible stacking configurations (ABC, ABA, BAB and CBA). Diffraction-limited spatial resolution makes it possible to image the switching of the stacking configurations. We find that the switching pathway is influenced not only by the competition among pinning centres—which localize domain walls at different interfaces—but also by a free-carrier screening effect linked to chemical doping. These findings highlight the importance of managing domain walls, pinning centres and doping levels in sliding ferroelectric devices, offering insights for further development in sensing and computing applications. The work studies the switchable excitonic response in trilayer 3R-MoS2 and shows that the polarization switching pathway in multilayer sliding ferroelectrics results from interactions between domain walls, pinning centres and free-carrier screening.