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

Abstract

In this work, it is considered a hybrid nanostructure composed by a quantum dot coupled to two ferromagnetic leads and a superconductor lead. It is shown that the zero-bias transmittance for the co-tunneling between the ferromagnetic leads presents Fano anti-resonances due to the destructive interference between the two spin channels mixing by the relative orientation of the magnetizations in the leads. When the superconductor is coupled to the system, electron-hole correlations between different spin states lead to a resonance in the place of the dip appearing in the transmittance. Such an effect is accompanied by two Fano anti-resonances explained by a "leakage" of conduction channels from the co-tunneling to the Andreev transport. In the non-equilibrium regime, correlations within the quantum dot introduce a dependence of the resonance condition on the finite bias applied to the ferromagnetic leads. However, it is still possible to observe signatures of the same interference effect in the electrical current.

Photon-assisted tunneling in a hybrid junction based on a quantum dot coupled to two ferromagnets and a superconductor

“…Effects due to interplay between direct Andreev reflection (AR) scattering , crossed Andreev reflection (CAR) processes, and electron tunneling (ET) in multiterminal hybrid junctions have been investigated in a number of theoretical as well as experimental works . Such devices have been proved to offer the possibility of manipulating phase coherent transmission and thus these can serve, e.g., as Andreev interferometers , the source of entangled states of electrons , or as the Cooper pair splitters .…”

“…The efforts have been focused mainly on investigating the transport features of planar hybrid structures consisting of a superconductor (S) attached to two or more probe electrodes being either normal (N) metals or ferromagnets (F). In a few papers discussion has been extended into three‐terminal junctions based on a quantum dot (QD) coupled to one superconducting and two non‐magnetic or ferromagnetic external leads (the //QD/S system). In particular, a specific magnetoresistance called Andreev reflection magnetoresistance (ARMR), an analogous characteristics to the tunnel magnetoresistance (TMR) in non‐hybrid /QD/ junctions, was analyzed .…”

“…It was shown that the fidelity of split Cooper pair electrons can be tuned by bias and gate voltages and thus such systems can be sources of fully entangled pairs of electrons extracted from superconductor and transmitted into normal terminals. Most recently also the interference effects on the //QD/S system were studied and modifications of the Fano resonances due to the presence of the superconductor terminal were discussed .…”

Transport through hybrid superconducting/ferromagnetic double-path junction

“…The relation between charge and spin degrees of freedom may be easily exploited in ferromagnetic/superconductor (F/S) nanostructures [1][2][3][4][5][6][7][8][9][10][11][12][13] The ferromagnetism breaks the spin symmetry while superconductivity breaks the electron-hole symmetry. In a superconductor the Cooper pairs, responsible for the superconducting features, have the same energy separated from the excited states by an energy gap.…”