Orbital dependent Coulomb drag in electron-hole bilayer graphene heterostructures

We report Coulomb drag studies in an electron-hole bilayer graphene heterostructure in a magnetic field, where the orbital, spin, and valley degrees of freedom are lifted by the combined effects of exchange interaction, Zeeman energy, and vertical displacement field. Our device enables the application of a large vertical displacement field in both layers. In addition to the well-established strong Coulomb drag between the Landau levels with an orbital quantum number N = 0, we observe a Coulomb drag signal between the N = 1 Landau levels under a suitable vertical displacement field. As the displacement field increases further, the Coulomb drag signal between N = 1 Landau levels weakens, and a Coulomb drag signal emerges between the N = 0 and N = 1 Landau levels. These findings suggest the important role of the orbital index and vertical displacement field in interlayer Coulomb interaction within the quantum Hall regime of coupled bilayer systems.