Quantum Hall drag of exciton condensate in graphene

Abstract

Exciton condensate is a Bose-Einstein condensate (BEC) of electron and hole pairs bound by the Coulomb interaction1,2. In an electronic double layer (EDL) under strong magnetic fields, filled Landau states in one layer bind with empty states of the other layer to form exciton condensate3–9. Here we report exciton condensation in bilayer graphene EDL separated by hexagonal boron nitride (hBN). Driving current in one graphene layer generates a near-quantized Hall voltage in the other layer, signifying coherent exciton transport4,6. Owing to the strong Coulomb coupling across the atomically thin dielectric, quantum Hall drag in graphene appears at a temperature ten times higher than previously observed in GaAs EDL. The wide-range tunability of densities and displacement fields enables exploration of a rich phase diagram of BEC across Landau levels with different filling factors and internal quantum degrees of freedom. The observed robust exciton condensation opens up opportunities to investigate various many-body exciton phases.