Tunable spin-dependent Andreev reflection in a four-terminal Aharonov-Bohm interferometer with coherent indirect coupling and Rashba spin-orbit interaction

Long Bai,Chen-Long Duan,Rong Zhang

doi:10.1186/1556-276x-7-670

Long Bai, Chen-Long Duan + Show 1 more

Open Access

https://doi.org/10.1186/1556-276x-7-670

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Abstract

Using the nonequilibrium Green’s function method, we theoretically study the Andreev reflection(AR) in a four-terminal Aharonov-Bohm interferometer containing a coupled double quantum dot with the Rashba spin-orbit interaction (RSOI) and the coherent indirect coupling via two ferromagnetic leads. When two ferromagnetic electrodes are in the parallel configuration, the spin-up conductance is equal to the spin-down conductance due to the absence of the RSOI. However, for the antiparallel alignment, the spin-polarized AR occurs resulting from the crossed AR (CAR) and the RSOI. The effects of the coherent indirect coupling, RSOI, and magnetic flux on the Andreev-reflected tunneling magnetoresistance are analyzed at length. The spin-related current is calculated, and a distinct swap effect emerges. Furthermore, the pure spin current can be generated due to the CAR when two ferromagnets become two half metals. It is found that the strong RSOI and the large indirect coupling are in favor of the CAR and the production of the strong spin current. The properties of the spin-related current are tunable in terms of the external parameters. Our results offer new ways to manipulate the spin-dependent transport.

Highlights

A quantum dot (QD) is an artificially low-dimensional structure that can be filled with electrons
The positions of peaks for AP alignment are shifted with α = 1. These results indicate that the coherent indirect coupling and the Rashba spin-orbit interaction (RSOI) play an important role in determining the feature of the Andreev reflection (AR) conductance spectra
Under the introduction of the Andreevreflected tunneling magnetoresistance (ARTMR), we find that the sign of the ARTMR versus the magnetic flux keeps invariable for different parameter α, but the convex shape of the ARTMR depends distinctly on the sign of the parameter α

Summary

Introduction

A quantum dot (QD) is an artificially low-dimensional structure that can be filled with electrons (or holes). Kubo and co-workers calculated the shot noise and Kondo effect in a DQD structure with the coherent indirect coupling. Their results demonstrate that the coherent indirect coupling can generate a novel antiferromagnetic exchange phenomenon [24]. Trocha and Barnasstudied theoretically the spin-dependent transport through a DQD coupled to ferromagnetic leads. The RSOI results from a relativistic effect at the low speed limit, and it can couple the electron spin to its orbital motion, providing a possible way to control the spin degree of freedom by means of an external electric field. The coherent indirect coupling and the RSOI make the quantum transport through the QD systems rich and varied [26,27,28,29,30]

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