|
A DC charge current can be driven through a mesoscopic conductor in the absence of an applied transport voltage by changing periodically in time some of the properties of the conductor. This transport mechanism is known as pumping. If the time-dependent parameters vary slowly as compared to the characteristic internal time scales of the system, pumping is adiabatic, and the average transmitted charge per cycle does not depend on the detailed timing of the cycle, but only on its area. For systems where the electron-electron interaction can be neglected, there is a well established formalism, based on the scattering approach to mesocopic transport, to compute the pumped current. The situation is more complicated when the interaction between the electrons becomes important, since the scattering approach cannot be employed any longer. As a paradigmatic system to investigate adiabatic pumping in the presence of electron-electron interaction we consider a spin-degenerate single-level quantum dot with Coulomb repulsion, tunnel-coupled to leads.
We present two different methods to compute the pumped current through such systems: First, by means of a non-equilibrium Green's function formalism we derive an approximated formula which relates the pumped charge to the instantaneous local Green's function of the dot [1]; Second, we develop a real-time diagrammatic approach to adiabatic pumping performing a systematic perturbative expansion in the tunnel coupling [2]. Furthermore, in order to investigate quantum-interference effects in pumping through interacting quantum dots, we consider an Aharonov-Bohm interferometer with a dot embedded in one of the arms and we compute the current by means of the real-time diagrammatic technique.
[1] J. Splettstoesser, M. Governale, J. König, and R. Fazio, Phys. Rev. Lett. 95, 246803 (2005). [2] J. Splettstoesser, M. Governale, J. König, and R. Fazio, Phys. Rev. B 74, 085305 (2006). |
|