Surface plasmon in a two-dimensional Anderson insulator with interactions.

We study the effect of interactions on the zero-temperature a.c. conductivity of 2D Anderson insulator at low frequencies. We show that the enhancement of the real part of conductivity due to the Coulomb correlations in the occupation numbers of localized states results in the change of the sign of imaginary part within a certain frequency range. As a result, the propagation of a surface plasmon in a localized system becomes possible. We analize the dispersion law of the plasmon for the two cases: unscreened Coulomb interactions and the interactions screened by a gate electrode spaced by some distance from the electron plane.