Many-Body Interactions in the Cyclotron Resonance of Encapsulated Graphene

We present observations of interband Landau level transitions in high-mobility graphene encapsulated in hexagonal boron nitride by way of Fourier-transform infrared magneto-spectroscopy. By varying the carrier density, n, at constant magnetic field, B, we observe a non-monotonic dependence of the transition energies on the Landau level filling factor, $\nu \propto$ n/B. These findings support the idea that electron-electron interactions contribute to the Landau level transition energies in graphene, beyond the single-particle picture. A splitting of transitions involving the zeroth Landau level is interpreted as a Dirac mass arising from the coupling of the graphene and hBN lattices. Additionally, we report recent work on the intraband Landau level resonances in both encapsulated graphene and graphene on silicon dioxide.