Simulation of the phononless hopping in a Coulomb glass

The phononless hopping conductivity of a disordered system with localized states is studied in a broad range of frequencies by straightforward computer simulations taking into account Coulomb interactions. At sufficiently low temperatures, the conductivity is determined by the zero-phonon absorption of the photon by pairs of states. The laser frequency dependence of the conductivity is examined and compared with the analytical model of Efros and Shklovskii and with recent experimental data obtained on Si:P. The range of parameters is determined, for which the conductivity dependence on photon energy best reproduces the experimental results.