Density of States in Two-DimensionalSquare Lattices Around Half Filling with Strong Impurities

Abstract

We calculate the lowest-order quantum-interference correction tothe density of states (DOS) of weakly-disordered two-dimensional(2D) tight-binding square lattices around half filling. Theimpurities are assumed to be randomly distributed on smallfractions of the sites, and have a strong potential yielding aunitary-limit scattering. In addition to the usual diffusive modesin the retarded-advanced channel, there appear diffusive πmodes in the retarded-retarded (or advanced-advanced) channel dueto the existence of particle-hole symmetry. It is found that theπ-mode diffuson gives rise to a logarithmic suppression to theDOS near the band center, which prevails over the positivecorrection contributed by π-mode cooperon. As a result, theDOS is subject to a negative total correction. This result isqualitatively different from the divergent behavior of the DOS atthe band center predicted previously for disordered 2Dtwo-sublattice models with the particle-hole symmetry.