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

TL;DR

This paper theoretically investigates how different geometries of double quantum dots affect their conductance, shot noise, and tunnel magnetoresistance, revealing geometry-dependent transport behaviors and potential for geometry identification.

Contribution

It introduces a comprehensive analysis of transport properties in various double quantum dot geometries using the real-time diagrammatic technique, highlighting geometry-specific effects.

Findings

Strong TMR dependence on electron occupation in series DQDs

Super-Poissonian shot noise in Coulomb blockade regime

Enhanced TMR and shot noise in T-shaped 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.