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

Abstract

The electric current and the magnetoresistance effect are studied in a double quantum-dot system, where one of the dots QD a is coupled to two ferromagnetic electrodes (F 1 , F 2 ), while the second QD b is connected to a superconductor S. For energy scales within the superconductor gap, electric conduction is allowed by Andreev reflection processes. Due to the presence of two ferromagnetic leads, non-local crossed Andreev reflections are possible. We found that the magnetoresistance sign can be changed by tuning the external potential applied to the ferromagnets. In addition, it is possible to control the current of the first ferromagnet (F 1 ) through the potential applied to the second one (F 2 ). We have also included intradot interaction and gate voltages at each quantum dot and analyzed their influence through a mean field approximation. The interaction reduces the current amplitudes with respect to the non-interacting case, but the switching effect still remains as a manifestation of quantum coherence, in scales of the order of the superconductor coherence length.

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

“…We observe Fano-like resonances appearing in the transmittance due to the interplay between different spin-channels and the Andreev bound states within the QD. In spite of transport properties have already been addressed in literature [23,31], the Fano-like interference reported here was not at all discussed in previous works. A similar pattern in the transmittance of a double QD coupled to non-magnetic leads [32] was considered but in that case it was a result of Fano interference between different paths for the transport.…”

“…This point has been discussed in depth in Ref. [31]. When the orientation angle θ is changed from 0 to π the crossed AR dominates the transport and the current is fully carried by crossed AR for full polarization.…”

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

“…4e. As shown in previous works 47,48 , this asymmetry is crucial for the transport since the Cooper pairs are formed by injecting two electrons with opposite spins and energy signs at once into the superconductor. In this way, the current being injected into the superconductor is determined by smaller peak of the transmittance.…”

Transport properties of proximitized double quantum dots

“…Other options of DQD with SC and N leads connection are also considered, e.g. connection of the first dot to two metallic leads and the second dot to the SC lead [11,12,19,23,25]. In such systems, there are possible both the normal electron transfers (when the single electron transfers between both normal metallic electrodes) and direct (DAR) and crossed (CAR) Andreev reflections (when electrons of the Cooper pair tunnel into SC lead and the holes tunnel to the same (DAR) or the second (CAR) metallic lead).…”