Layer Specific Anomalous Screening in an Unconventional Ferroelectric System

In our previous work, we reported the observation of emergent ferroelectricity in bilayer graphene/BN moiré vdW heterostructures. The rich and complex ferroelectric response as a function of the displacement field and electron filling is distinct from any previously reported 2D ferroelectrics.  However, despite its unique features and potential for next-generation electronic devices, much remains to be explored and understood in this new platform of unconventional ferroelectric systems. In order to unveil the underlying mechanism, we have performed a more systematic study. Through a more precise angle control, we aim to narrow down the key ingredients that will allow us to deliberately control and engineer the ferroelectricity. Assisted by detailed Hall density measurements, we manage to find evidence that points toward a layer specific charge reservoir, which could be responsible for the unconventional and rather striking ferroelectric response. Based on our observations, we further propose an intuitive picture in an attempt to capture the rich physics and explain the intricate pattern of the layer specific anomalous screening behavior. With our work, we hope to provoke further interests towards a wider class of unconventional ferroelectric systems originating from a controlled layer specific charge reservoir and subsequently lay the foundation for new potential electronic applications.