Longitudinal Conductivity of Bilayer Graphene in the Integer Quantum Hall Regime

We investigate the frequency dependent conductivity of disordered bilayer graphene near neutral filling, in a strong magnetic field. Absent Zeeman coupling, and with two independent valleys, a graphene bilayer's lowest Landau level is eightfold-degenerate, comprising two Landau orbitals of equal energy. Its spectral properties are altered by an inter-layer bias potential, which can open a gap between the constituent orbitals. We establish the dependence of the one and two-particle disorder-averaged Greens' functions on inter-layer bias, and show that the longitudinal conductivity exhibits the signature of disorder-induced Landau orbital mixing.