A simple model of ac hopping conductivity in disordered solids

Using the CTRW approximation the simplest possible nontrivial model of ac hopping conductivity in disordered solids, is constructed. The model predicts universality of the frequency-dependent conductivity, independent of temperature, chemical composition, and conductivity mechanism, in resonably good agreement with experiments. It is shown that all qualitative features of experimental ac hopping conductivity can be understood within the model.