Coulomb drag between disordered two-dimensional electron-gas layers

We derive and evaluate expressions for the frictional Coulomb drag between disordered two-dimensional electron-gas layers. Our derivation is based on the memory-function formalism and the expression for the drag reduces to previously known results in the ballistic limit. We find that Coulomb drag is appreciably enhanced by disorder at low temperatures when the mean free path within a layer is comparable to or shorter than the layer separation. In high-mobility two-dimensional electron-gas systems, where the drag has been studied experimentally, the effect of disorder on the drag is negligible at attainable temperatures. We predict that an enhancement due to disorder and a crossover in the temperature dependence and layer-separation dependence will be observable at low temperatures in moderate- and low-mobility samples.