Nonlinear conductivity of two-dimensional Coulomb glasses

We have studied the nonlinear conductivity of two- dimensional Coulomb glasses. We have used a Monte Carlo algorithm to simulate the dynamic of the system under an applied electric field E. We found that in the nonlinear regime the site occupancy in the Coulomb gap follows a Fermi- Dirac distribution with an effective temperature T-eff, higher than the phonon bath temperature T. The value of the effective temperature is compatible with that obtained for slow modes from the generalized fluctuation- dissipation theorem. The nonlinear conductivity for a given electric field and T is fairly similar to the linear conductivity at the corresponding T-eff. We found that the dissipated power and the effective temperature are related by an expression of the form (T-eff(alpha)-T-alpha)T-eff(beta-alpha).