1/f noise in electron glasses

We show that 1/f noise is produced in a three-dimensional electron glass by charge fluctuations due to electron hopping between isolated sites and a percolating network at low-temperatures. The low-frequency noise spectrum goes as ω^-α with α slightly larger than 1. This result together with the temperature dependence of α and the noise amplitude are in good agreement with the recent experiments. These results hold true both with a flat, noninteracting density of states and with a density of states that includes the Coulomb interactions. In the latter case, the density of states has a Coulomb gap that fills in with increasing temperature. For a large Coulomb gap width, this density of states gives a dc conductivity with a hopping exponent of ≈0.75 which has been observed in recent experiments. For a small Coulomb gap width, the hopping exponent ≈0.5.