Controle de Corrente de Spin em Pontos Quânticos na Presença de Tensões de Porta Moduladas no Tempo

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

09/08/2011

RESUMO

Since Loss &DiVincenzo proposal to use confined electron spins in quantum dots (QDs) as a building block for qubits in solid state systems, spin-dependent transport in QDs has attracted a lot of attention. The interest for this system increased even further with the recent experimental developments to coherently control (initialization-manipulation-read out) of single electron spins in QDs. Additionally, quantum dots attached to leads provide a wealth environment to study fundamental physical aspect of nonequilibrium quantum systems with spin-dependent and many-body correlations. In our study we analyze the electric transport in a nanostructure consisting of two ferromagnetic materials separated by a single quantum dot, coupled via tunneling barriers. Using non-equilibrium Green function technique we calculate physical quantities such as current, spectral function, transmission coefficient and tunnel magnetoresistance (TMR). By applying a gate potential that oscillates in time, additional photon-assisted channels emerge, thus introducing additional transmission channels. All these transport quantities are calculated in both parallel and antiparallel alignments of the leads magnetization. Additionally, Zeeman splitting of the dot level is considered. The dot levels are positioned inside and outside of the conduction window of the system. Our main results include the appearance of photon-assisted peaks in the average spin-resolved currents that allows the control of the current polarization via the gate frequency. Moreover, the tunnel magnetoresistance presents a variety of photon-assisted peaks and dips depending on the gate frequency. In particular, the TMR develops negative values for some particular frequency values.

ASSUNTO(S)

funções de green de não-equilíbrio tunelamento fótonassistido corrente de spin tensão de porta desdobramento zeeman fisica pontos quânticos spintrônica non-equilibrium green functions quantum dots photon-assisted tunneling spin current gate voltage zeeman spliting

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