Quantum Hall drag of exciton condensate in graphene

Abstract

An exciton condensate is a Bose-Einstein condensate of electron and hole pairs bound by the Coulomb interaction1,2. In an electronic double layer (EDL) subject to strong magnetic fields,filledLandaustatesinonelayerbindwithemptystatesof the other layer to form an exciton condensate3-9. Here we report exciton condensation in a bilayer graphene EDL separated by hexagonal boron nitride. Driving current in one graphene layer generates a near-quantized Hall voltage in the other layer, resulting in 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 a GaAs EDL. The wide-range tunability of densities and displacement fields enables exploration of a rich phase diagram of Bose-Einstein condensates 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.