Spin pumping with quantum dots

Abstract

The purpose of this paper is to discuss how lateral semiconductor quantum dots can be used as pumps to produce spin polarised currents, by exploring quantum phase coherence phenomena. Electronic transport in phase coherent or mesoscopic systems has been intensively studied for more than three decades. While there is a substantial understanding of the stationary regime, much less is known about phase-coherent non-equilibrium transport when pulses or ac perturbations are used to drive electrons at low temperatures and at small length scales. However, about 20 years ago Thouless proposed to drive non-dissipative currents in quantum systems by applying simultaneously two phase-locked external perturbations. The so-called adiabatic pumping mechanism has been revived in the last few years, both theoretically and experimentally, in part because of the development of lateral semiconductor quantum dots. Here we show how open dots can be used to create spin-polarised currents with little or no net charge transfer. The pure spin pump we propose is the analog of a charge battery in conventional electronics and may provide a needed circuit element for spin-based electronics. We also briefly discuss other relevant issues such as rectification and decoherence and point out possible extensions of the pumping mechanism to closed quantum dots.