Crossed conductance in ferromagnet/superconductor/ferromagnet double junctions: Role of out-of-equilibrium populations

Abstract

We discuss a model of Ferromagnet / Superconductor / Ferromagnet (FSF) double junction in which the quasiparticles are not in equilibrium with the condensate in a region of the superconductor containing the two FS contacts. The role of geometry is discussed, as well as the role of a small residual density of states within the superconducting gap, that allows a sequential tunneling crossed current. With elastic quasiparticle transport and the geometry with lateral contacts, the crossed conductances in the sequential tunneling channel are almost equal in the normal and superconducting phases, if the distance between the FS interfaces is sufficiently small. The sequential tunneling and spatially separated processes (the so-called crossed Andreev reflection and elastic cotunneling processes) lead to different signs of the crossed current in the antiparallel alignment for tunnel interfaces.

Magnetoresistance and transistor-like behavior of a double quantum-dot via crossed Andreev reflections

“…This feature has been explored by Deutscher and Feinberg 2 to propose a non-local Andreev reflection (called crossed AR), where two electrons of different leads can combine into a Cooper pair if the distance between these leads is smaller than the coherence length. Since this proposal, there has been a profusion of works exploring crossed AR in different geometries [3][4][5][6][7][8][9][10][11] , resonant nanostructures involving quantum dots [12][13][14][15][16][17] , different conduction regimes 18,19 (ballistic and diffusive), and addressing more fundamental a) Electronic mail: ecosta@dfq.feis.unesp.br b) Electronic mail: cabrera@ifi.unicamp.br questions, e.g., the entanglement of the quasiparticles in different leads [20][21][22][23][24][25] . Within this vast set of hybrid nanostructures, systems composed by double quantum dots (QDs) are very promising, since this association can serve as a model of diatomic molecules [26][27][28] .…”

Fano effect and Andreev bound states in a hybrid superconductor–ferromagnetic nanostructure

“…The electrons are also submitted to Coulomb correlations within the QD. All these features lead to rather complex spectral properties for the QD [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. More specifically, a multi-peak structure has been observed in a F-QD-S nanostructure caused by the interplay between Coulomb correlations and Zeeman splitting due to an external magnetic field [18].…”

Interference effects induced by Andreev bound states in a hybrid nanostructure composed by a quantum dot coupled to ferromagnetic and superconductor leads

“…In these systems one is able to investigate purely quantum phenomena and the conduction of electrical current with a discrete flux of charges through the QDs 17 . As a result, new phenomena may arise concerning the transport properties of these systems [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . A particular feature of these hybrid F/S systems is the current dependence on QD spectral properties, besides the ferromagnet polarization.…”