A T-shaped double quantum dot system as a Fano interferometer: interplay of coherence and correlation upon spin currents

TL;DR

This paper investigates how quantum interference and electron correlations in a T-shaped double quantum dot system influence spin currents, revealing complex behaviors like Fano resonances, localization effects, and control via gate voltages.

Contribution

It introduces a detailed analysis of spin transport in a T-shaped quantum dot device considering both Fano interference and Coulomb interactions, highlighting their interplay in spin current modulation.

Findings

Spin currents depend on lead polarization orientation.

Coulomb interactions suppress Fano resonances and can induce negative spin conductance.

Gate voltages enable control over spin and charge currents.

Abstract

Based on Keldysh non-equilibrium Green function method, we have investigated spin current production in a hybrid T-shaped device, consisting of a central quantum dot connected to the leads and a side dot which only couples to the central dot. The topology of this structure allows for quantum interference of the different paths that go across the device, yielding Fano resonances in the spin dependent transport properties. Correlation effects are taken into account at the central dot and handled within a mean field approximation. Its interplay with the Fano effect is analyzed in the strong coupling regime. Non-vanishing spin currents are only obtained when the leads are ferromagnetic, the current being strongly dependent on the relative orientation of the lead polarizations. We calculate the conductance (spin and charge) by numerically differentiating the current, and a rich structure is obtained as a manifestation of quantum coherence and correlation effects. Increase of the Coulomb interaction produces localization of states at the side dot, largely suppressing Fano resonances. The interaction is also responsible for the negative values of the spin conductance in some regions of the voltage near resonances, effect which is the spin analog of the Esaki tunnel diode. We also analyze control of the currents via gate voltages applied to the dots, possibility which is interesting for practical operations.