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.