POSSIBILITY OF 2 TYPES OF LOCALIZED STATES IN A 2-DIMENSIONAL DISORDERED LATTICE

We report results of our numerical calculations, based on the equation of motion method, of dc electrical conductivity, and of density of st ates for up to 40 X 40 two-dimensional square lattices modeling a tigh t-binding Hamiltonian for a binary (AB) compound, disordered by random ly distributed B vacancies up to 10%. Our results indicate strongly lo calized states away from band centers separated from the relatively we akly localized states towards midband. This is in qualitative agreemen t with the idea of a ''mobility edge'' separating exponentially locali zed states from the power-law localized states as suggested by the two -parameter scaling theory of Kaveh in two dimensions. An alternative e xplanation, consistent with one-parameter scaling theory, is that the observed numerical effects may arise as a consequence of the variation of the localization length over the band.