Spin filtering through excited states in double quantum dot pumps

TL;DR

This paper demonstrates how ac-driven double quantum dots can be used as tunable spin filters by controlling parameters like amplitude and frequency, with excited states enabling bipolar filtering and potential measurement of spin decoherence times.

Contribution

It introduces a method to control spin polarization in quantum dot pumps via ac field tuning and links current peak features to spin decoherence measurement.

Findings

Current peaks are associated with specific spin polarizations.

Tuning ac parameters enables bipolar spin filtering.

Peak widths can determine spin decoherence time T2.

Abstract

Recently it has been shown that ac-driven double quantum dots can act as spin pumps and spin filters. By calculating the current through the system for each spin polarization, by means of the time evolution of the reduced density matrix in the sequential tunneling regime (Born-Markov approximation), we demonstrate that the spin polarization of the current can be controlled by tuning the parameters (amplitude and frequency) of the ac field. Importantly, the pumped current as a function of the applied frequency presents a series of peaks which are uniquely associated with a definite spin polarization. We discuss how excited states participating in the current allow the system to behave as a bipolar spin filter by tuning the ac frequency and intensity. We also discuss spin relaxation and decoherence effects in the pumped current and show that measuring the width of the current vs frequency peaks allows to determine the spin decoherence time $T_{2}$.