LINEAR-RESPONSE THEORY OF COULOMB DRAG IN COUPLED ELECTRON-SYSTEMS

We report a fully microscopic theory for the transconductivity, or, eq uivalently, the momentum transfer rate, of Coulomb coupled electron sy stems. We use the Kubo linear-response formalism and our main formal r esult expresses the transconductivity in terms of two fluctuation diag rams, which are topologically related but not equivalent to the Aslama zov-Larkin diagrams known from superconductivity. Results reported els ewhere are shown to be special cases of our general expression; specif ically, we recover the Boltzmann equation result in the semiclassical clean limit and the memory function results for dirty systems with con stant impurity scattering rates. Furthermore, we show that for energy- dependent relaxation times, the final result is not expressible in ter ms of standard density-response functions. Other results include (i) a t T = 0, the frequency dependence of the transfer rate is found to be proportional to Omega and Omega(2) for frequencies below and above the impurity scattering rate, respectively, and (ii) the weak localizatio n correction to the transconductivity is given by delta sigma(21)(WL)p roportional to delta sigma(11)(WL) +delta sigma(22)(WL).