Conductance relaxation in the Electron-Glass; Microwaves versus infra-red response

We study the time-dependent conductance of electron-glasses excited by electromagnetic radiation at microwaves (MW) and infra-red frequencies. In either case the conductance G is enhanced during exposure but its time dependence after the radiation is turned off is qualitatively different depending on the frequency. For comparison, results of excitation produced by a gate-voltage and temperature changes are also shown. The glassy nature of the system allows us to demonstrate that the MW-enhanced conductance is not due to heating. These findings are discussed in terms of an energy E_{c} that characterizes the equilibrium charge distribution of the electron-glass.