Electrostatically Gate-defined Structures in Graphene

Graphene, a tunable 2D material, can support novel fractional quantum hall (FQH) states with large energy gaps, which makes it an emerging platform to study fractional or even non-Abelian statistics with quantum Hall interferometer. However, electrostatic confinement, which is required to fine-tune interference area, is elusive in graphene since it is a gapless semiconductor. Moreover, experience from GaAs/GaAlAs quantum well system indicates electrostatic gating may degrade device quality. Here we present hBN-encapsulated monolayer and bilayer graphene gate defined devices with graphite gates on both sides, without sacrificing FQH quality. With electrostatic gating, we define the active device region by putting the off-regions at nu=0, which has energy gap both in bulk and edge. We observed in transport, FQH states at magnetic field as low as 6 T with enhanced energy gaps, the presence of four-flux states and reentrant integer quantum Hall states which arise from electron solid phases. Our result paves the way for electrostatic constrictions under the FQH regime in graphene.