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

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.

Splitting efficiency and interference effects in a Cooper pair splitter based on a triple quantum dot with ferromagnetic contacts

“…One can generally expect an enhancement of CAR processes when the magnetic configuration changes from the parallel to the antiparallel one, since then the nonlocal processes are mainly determined by a fast majority spin channel, while the local processes are slower because they depend on the minority spin subband [32,57]. However, it turns out that this rule can depend on the position of dots' levels and interference effects [16,17,30,34,40,58]. Quantum interference can in fact make the situation quite counterintuitive and re- verse the role of CAR and DAR processes, as we discuss below.…”

“…In addition, we examine the impact of direct hopping between the dots forming the arms of the splitter on the spin-resolved transport properties of the system. Furthermore, the effects of the Rashba spinorbit interaction [18,19,[38][39][40][41][42] on the splitting efficiency η of the device are also discussed. We show that η greatly depends on the arrangement of magnetic moments of ferromagnetic leads and the positions of the quantum dots' levels.…”

Fano-type resonances induced by a boson mode in Andreev conductance

“…The model (1) can be generalized to more complex situations, for instance when both quantum dots are coupled to the external leads [16,23] and to the boson mode. For clarity, we focus on the case illustrated in Fig.…”

“…[6][7][8][9][10] This issue has been studied theoretically for the single quantum dot [11][12][13][14][15][16][17] (see also other references cited therein) and the double quantum dot heterojunctions. [18][19][20][21][22][23][24][25] Since nanoscopic objects (quantum dots, nanowires or molecules) are never entirely separated from their environment (e.g., photon [26] or vibron [27] quanta) therefore transport properties can reveal additional features originating from the constructive/destructive interference. In this work, we study the system (Fig.…”