Chiral symmetry and fermion doubling in the zero-mode Landau levels of massless Dirac fermions with disorder

The effect of disorder on the Landau levels of massless Dirac fermions is examined for the cases with and without the fermion doubling. To tune the doubling a tight-binding model having a complex transfer integral is adopted to shift the energies of two Dirac cones, which is theoretically proposed earlier and realizable in cold atoms in an optical lattice. In the absence of the fermion doubling, the $n=0$ Landau level is shown to exhibit an anomalous sharpness even if the disorder is uncorrelated in space (i.e., large K-K scattering). This anomaly occurs when the disorder respects the chiral symmetry of the Dirac cone.