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 nonparabolic 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 (${E}_{\mathrm{F}}$). 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 ${E}_{\mathrm{F}}$ of BLG. The CR magnetic field value shifted significantly when ${E}_{\mathrm{F}}$ 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.