Variable-range hopping within a fluctuating potential landscape

The effect of temporal and spatial potential-energy fluctuations on low-temperature dark dc conductivity in disordered materials is considered. Analytical models are formulated to treat the variable-range hopping in a disordered system of localized states whose energies are subjected to 1/ftemporal fluctuations. Long-range spatial potential fluctuations are described as a random distribution of intrinsic electric field. Temporal 1/ffluctuations are assumed either to be independent of carrier hopping or to be caused by the latter process. Both spatial and independent 1/ftemporal fluctuations are shown to yield temperature dependences of the conductivity much weaker than those predicted by the Mott law. Self-sustaining 1/ftemporal fluctuations caused by the carrier random walk lead to the crossover from Mott's T^-1/4to T^-1/3dependence with increasing temperature.