Spin-filtering through excited states in double-quantum-dot pumps

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 T2.

Photon assisted long-range tunneling

“…For completeness, we also plot the current obtained in the We compare the full numerics solution, obtained by the integration of Eq. (5) with the different approximations: the effective model for the tunnel coupling (13) and the rotating wave approximation (18). We also plot the current for the undriven case which only shows the central peak.…”

“…Photon assisted transport in nanostructures has been object of intense research 2 . We mention only those references close to this work in double barriers [5][6][7][8][9] and quantum dots 4,[10][11][12][13][14][15][16][17][18][19][20][21] . An additional and important effect of photon assisted tunneling is the renormalization of the tunnel couplings which become dependent on the parameters of the driving.…”

Green Function Techniques in the Treatment of Quantum Transport at the Molecular Scale

“…Finally, we want to mention briefly three important fields of research, that we do not consider in the present review: the theory of Kondo effect [228,229,230,205,231,232,233,234], spin-dependent transport [235,236,237,238,239], and time-dependent transport [83,240,241,242,243].…”

Spin correlations in spin blockade

“…Then, the triplet states have finite lifetimes due to photon absorption processes so that spin blockade is resolved [1,33]. A paradigmatic setup for which resonant ac-electric fields can lead to finite charge [34] or spin currents [16] even in the absence of a source-drain voltage (µ L = µ R = µ) is the spatially asymmetric pump configuration of the double dots sketched in figure 7. There the asymmetry is provided by the different intra-dot interactions U L > U R .…”