Andreev tunneling through a double quantum-dot system coupled to a ferromagnet and a superconductor: Effects of mean-field electronic correlations

Abstract

We study the transport properties of a hybrid nanostructure composed of a ferromagnet, two quantum dots, and a superconductor connected in series. By using the nonequilibrium Green's function approach, we have calculated the electric current, the differential conductance, and the transmittance for energies within the superconductor gap. In this regime, the mechanism of charge transmission is the Andreev reflection, which allows for a control of the current through the ferromagnet polarization. We have also included interdot and intradot interactions, and have analyzed their influence through a mean-field approximation. In the presence of interactions, Coulomb blockade tend to localize the electrons at the double-dot system, leading to an asymmetric pattern for the density of states at the dots, and thus reducing the transmission probability through the device. In particular, for nonzero polarization, the intradot interaction splits the spin degeneracy, reducing the maximum value of the current due to different spin-up and spin-down densities of states. Negative differential conductance appears for some regions of the voltage bias, as a result of the interplay of the Andreev scattering with electronic correlations. By applying a gate voltage at the dots, one can tune the effect, changing the voltage region where this novel phenomenon appears. This mechanism to control the current may be of importance in technological applications.

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

“…In the case in which crossed ARs are present, the effect of U on the spin-degeneracy is more complex in comparison to systems with two-terminals as the one studied in Ref. 62. To illustrate this point, a comparison between the responses of the present system and the twoterminal system of Ref.…”

Phonon-assisted Andreev reflection in a hybrid junction based on a quantum dot

“…In particular, the effects due to overlap of the phonon and main resonances for arbitrary Coulomb correlations are observed, the condition of the U -dependent enhancement of the conductance is determined in situation when electronphonon interactions tend to suppress the AR transmission. We also discuss another mechanism of occurrence of negative differential conductance (NDC) in hybrid tunneling devices, which is different from the one described previously for the Andreev tunneling through a double quantum dot attached to F and S external leads [9]. Consequently, the effect of oscillations of NDC is found to occur due to the phonon-assisted transmission in the AR regime and it is studied in the context of tunneling processes between the dot and differently polarized F electrode.…”

Current cross-correlations and waiting time distributions in Andreev transport through Cooper pair splitters based on a triple quantum dot system

“…1,2 One prominent class of hybrid nanoscale devices are quantum dots coupled to superconducting and normal contacts. [3][4][5][6][7][8][9][10] In this regard, particularly interesting is a three-terminal setup known as Cooper pair splitter (CPS), [11][12][13][14][15][16][17][18][19][20] which consists of one superconducting and two normal metallic leads. Such CPS devices provide the possibility to generate non-local pairs of entangled electrons in a controllable fashion.…”