Cyclotron Resonance in Dual-Gated Bilayer Graphene

We report observations of cyclotron resonance in boron nitride-encapsulated, dual-gated bilayer graphene by way of transmission infrared magnetospectroscopy. The inter-Landau level transitions -2 → 1 and 1 → 2 are studied at a fixed magnetic field of 13 T as a function of the Landau level filling factor, ν, and the layer symmetry-breaking perpendicular electric displacement field, D. Varying D at ν = 4 yields a direct and high-resolution measurement of the optical bandgap in bilayer graphene at low energies. For increasing D at ν = 0 we observe a varying number of transitions as the K and K’ valleys diverge, while a sharp change in the CR energies signals the transition to a layer polarized state at finite D. A detailed description of the data requires consideration of band parameters beyond the lowest order inter- and intra-layer hopping terms. Measurements at D = 0 reveal a pronounced electron-hole asymmetry and many-body interaction effects as ν is varied.