Interaction-induced charge and spin pumping through a quantum dot at finite bias

TL;DR

This paper studies how interactions in a quantum dot cause charge and spin to be pumped through it under adiabatic driving, revealing new effects at finite bias and magnetic fields with analytic formulas and potential for measuring junction asymmetry.

Contribution

It introduces a kinetic equation approach to analyze interaction-induced charge and spin pumping, extending previous scattering matrix methods and providing explicit formulas for various regimes.

Findings

Interaction-induced pumping occurs under periodic modulation of gate and bias voltage.

Pure spin pumping can be achieved at finite magnetic field and bias.

Pumped charge and spin saturate at large driving amplitudes, independent of cycle shape.

Abstract

We investigate charge and spin transport through an adiabatically driven, strongly interacting quantum dot weakly coupled to two metallic contacts with finite bias voltage. Within a kinetic equation approach, we identify coefficients of response to the time-dependent external driving and relate these to the concepts of charge and spin emissivities previously discussed within the time-dependent scattering matrix approach. Expressed in terms of auxiliary vector fields, the response coefficients allow for a straightforward analysis of recently predicted interaction-induced pumping under periodic modulation of the gate and bias voltage [Phys. Rev. Lett. 104, 226803 (2010)]. We perform a detailed study of this effect and the related adiabatic Coulomb blockade spectroscopy, and, in particular, extend it to spin pumping. Analytic formulas for the pumped charge and spin in the regimes of small and large driving amplitude are provided for arbitrary bias. In the absence of a magnetic field, we obtain a striking, simple relation between the pumped charge at zero bias and at bias equal to the Coulomb charging energy. At finite magnetic field, there is a possibility to have interaction-induced pure spin pumping at this finite bias value, and generally, additional features appear in the pumped charge. For large-amplitude adiabatic driving, the magnitude of both the pumped charge and spin at the various resonances saturate at values which are independent of the specific shape of the pumping cycle. Each of these values provide an independent, quantitative measurement of the junction asymmetry.