Effects of different geometries on the conductance, shot noise and tunnel magnetoresistance of double quantum dots

Abstract

The spin-polarized transport through a coherent strongly coupled double quantum dot (DQD) system is analyzed theoretically in the sequential and cotunneling regimes. Using the real-time diagrammatic technique, we analyze the current, differential conductance, shot noise and tunnel magnetoresistance (TMR) as a function of both the bias and gate voltages for double quantum dots coupled in series, in parallel as well as for T-shaped systems. For DQDs coupled in series, we find a strong dependence of the TMR on the number of electrons occupying the double dot, and super-Poissonian shot noise in the Coulomb blockade regime. In addition, for asymmetric DQDs, we analyze transport in the Pauli spin blockade regime and explain the existence of the leakage current in terms of cotunneling and spin-flip cotunneling-assisted sequential tunneling. For DQDs coupled in parallel, we show that the transport characteristics in the weak coupling regime are qualitatively similar to those of DQDs coupled in series. On the other hand, in the case of T-shaped quantum dots we predict a large super-Poissonian shot noise and TMR enhanced above the Julliere value due to increased occupation of the decoupled quantum dot. We also discuss the possibility of determining the geometry of the double dot from transport characteristics. Furthermore, where possible, we compare our results with existing experimental data on nonmagnetic systems and find qualitative agreement.

15 pages, 12 figures, accepted in Phys. Rev. B

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• Superconducting proximity effect and zero-bias anomaly in transport through quantum dots weakly attached to ferromagnetic leads
• Waiting time distribution revealing the internal spin dynamics in a double quantum dot
• Spin correlations in spin blockade
• Enhanced current noise correlations in a Coulomb-Majorana device
• Interplay between interference and Coulomb interaction in the ferromagnetic Anderson model with applied magnetic field
• Large voltage-tunable spin valve based on a double quantum dot
• Coherent switching by detuning a side-coupled quantum-dot system
• Pauli spin blockade with site-dependent g-tensors and spin-polarized leads
• The RKKY Interaction and the Nature of the Ground State of Double Dots in Parallel
• Tunnel magnetoresistance of a supramolecular spin valve
• Finite-frequency noise, Fano factor, $\Delta T$-noise and cross-correlations in double quantum dots
• Revealing the internal spin dynamics in a double quantum dot by periodic voltage modulation