Fig. 1: Ferroelectric hysteresis in monolayer graphene superlattices.

a Schematic of our device with asymmetric moiré interfaces and dual-gate structure. The red wavy line illustrates the moiré potential at top interface trapping holes (green balls) injected by the top gate (\({V}_{\text{t}}\)), which are bound by itinerant electrons (red balls) injected by the bottom gate (\({V}_{\text{b}}\)). The vertical arrow defines the positive electric field. Bottom panel shows conductive atomic force microscopy image of graphene/h-BN moiré superlattices. The scale bar is 50 nm. b, c Four-terminal longitudinal resistance \({R}_{{xx}}\) as a function of \({V}_{\text{t}}\) at fixed \({V}_{\text{b}}=0\) for monolayer graphene (b) and bilayer graphene (c) moiré superlattices. The arrows illustrate the sweep direction. d \({R}_{{xx}}\) as a function of \({V}_{\text{t}}\) by sweeping \({V}_{\text{t}}\) in various ranges (\({\left|{V}_{\text{t}}\right|}_{\max }\)) while fixing \({V}_{\text{b}}=0\). e \({R}_{{xx}}\) as a function of \({V}_{\text{b}}\) by sweeping \({V}_{\text{b}}\) in various ranges (\({\left|{V}_{\text{b}}\right|}_{\max }\)) while fixing \({V}_{\text{t}}=0\). The curves in (d) and (e) are vertically shifted for clarity. The forward and backward sweeps are shown in solid and dashed lines, respectively. The inset in (e) plots the difference of charge-neutrality points between forward and backward sweeps as a function of \({\left|{V}_{\text{b}}\right|}_{\max }\).