Theory of noncoherent spin pumps

We study electron pumps in the absence of interference effects paying attention to the spin degree of freedom. Electron-electron exchange interactions combined with a variation of external parameters, such as magnetic field and gate potentials, affect the compressibility-spin tensor whose components determine the noncoherent parts of the charge and spin pumped currents. An appropriate choice of the trajectory in the parameter space generates an arbitrary ratio of spin to charge pumped currents. After showing that when dephasing leads are added to a fully quantum coherent system the interference contribution diminishes, and the noncoherent (classical) contribution remains intact, we apply the theory of the classical term for several examples. We show that when exchange interactions are included one can construct a source of pure spin current, with a constant magnetic field and a periodic variation of gate potentials only. We discuss the possibility to observe it experimentally in GaAs heterostructures.