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 a vertical displacement field. Our device enables the application of a large vertical displacement field across 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 vertical 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 roles of the orbital index and the vertical displacement field in interlayer Coulomb interaction within the quantum Hall regime of coupled bilayer systems.