Terahertz conductivity of graphene on boron nitride

The conductivity of graphene on a boron nitride substrate exhibits features in the terahertz (THz) and infrared (IR) frequency regimes that are associated with the periodic moire pattern formed by weakly coupled twodimensionalmaterials. The THz and IR features are strongest when the two honeycomb lattices are orientationally aligned, and in this case they are Pauli blocked unless the Fermi level is close to +/- 150 meV relative to the graphene sheet Dirac point. Because the transition energies between moire bands formed above the Dirac point are small, ac conductivity features in n-doped graphene tend to be overwhelmed by the Drude peak. The substrate-induced band splitting is larger at energies below the Dirac point, however, and it can lead to sharp features at THz and IR frequencies in p-doped graphene. In this paper, we focus on the strongest few THz and IR features, explaining how they arise from critical points in the moire-band joint density of states, and commenting on the interval of Fermi energy over which they are active.