Anomalous Gate-tunable Capacitance in Van der Waals Heterostructures

TL;DR

This study reveals anomalous gate-tunable capacitance and hysteresis in graphene/hBN heterostructures, suggesting the ferroelectricity originates from hBN, which could lead to innovative memory device designs.

Contribution

It demonstrates that the anomalous ferroelectricity and capacitance in graphene/hBN heterostructures are likely due to the dielectric hBN, challenging previous assumptions about moiré potential effects.

Findings

Observed two types of hysteresis in TDBLG/hBN heterostructures.

Found identical phenomena in control graphene heterostructures without moiré potential.

Indicated hBN dielectric properties as the origin of ferroelectricity.

Abstract

The ferroelectricity emerging in non-polar graphene/hexagonal boron nitride (hBN) heterostructures has drawn considerable attention because of its fascinating properties and promising high-frequency electrical polarization switching. Yet, the underlying mechanism is still under debate. Here in twisted double bilayer graphene (TDBLG) aligned with its neighboring hBN, we observed two types of hysteresis - delayed hysteresis in top gate induced by the anomalous screening, and advanced hysteresis in back gate caused by the anomalous gate-tunable capacitance. To investigate the role played by moir\'e potential in the anomalous hysteresis, we studied a moir\'eless graphene heterostructure as control experiment. Unexpectedly, we observed exactly the same phenomena in this control device. Our findings suggest that the anomalous ferroelectricity in graphene/hBN heterostructures may originate from the dielectric material hBN, calling for further structural investigations on hBN. The observation of gate-tunable capacitance provides more insights in the mysterious ferroelectricity in graphene/hBN heterostructures, and should enable new design of memory devices such as memcapacitor based on tunable capacitance.