Probing many-body interactions in the cyclotron resonance of h-BN/bilayer graphene/h-BN

Unlike a conventional two-dimensional electron gas system, which has parabolic band structure, the non parabolic band dispersion of mono-to few-layer graphene violates Kohn's theorem. Thus, Landau levels (LLs) in graphene are sensitive to many-body interactions. This modifies the LL spacing, depending on the location of the Fermi energy (E-F). Such effects have been extensively studied in h-BN/monolayer graphene/h-BN through observation of inter-LL optical transitions known as cyclotron resonances (CRs). However, thus far, the influence of many-body interactions on the CR of bilayer graphene (BLG) has been rarely studied, even though BLG also possesses nonparabolic band dispersion. Here, we investigate CR in the h-BN/BLG/h-BN structure via magneto-photothermoelectric measurements under infrared laser irradiation. This method enables sensitive detection of cyclotron resonances while tuning E-F of BLG. The CR magnetic field value shifted significantly when E-F of BLG approached the charge-neutrality point (the Dirac point, DP). We attribute this to a change in the Fermi velocity of BLG near the DP, which occurs as a result of many-body interactions.