The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads

TL;DR

This paper investigates spin-dependent electron transport in chains of three quantum dots coupled to magnetic leads, revealing how Coulomb correlations influence tunnel magnetoresistance, shot noise, and conductance in different regimes.

Contribution

It provides a detailed numerical analysis of TMR, shot noise, and conductance in quantum dot chains, highlighting the impact of interdot Coulomb correlations on transport properties.

Findings

Strong correlations can cause negative TMR and NDC.

Weak correlations lead to positive TMR not exceeding Julliere's value.

Transport behavior depends on high-spin states and tunneling rules.

Abstract

We analyze numerically the spin-dependent transport through coherent chains of three coupled quantum dots weakly connected to external magnetic leads. In particular, using the diagrammatic technique on the Keldysh contour, we calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the sequential and cotunneling regimes. We show that transport characteristics greatly depend on the strength of the interdot Coulomb correlations, which determines the spacial distribution of electron wave function in the chain. When the correlations are relatively strong, depending on the transport regime, we find both negative TMR as well as TMR enhanced above the Julliere value, accompanied with negative differential conductance (NDC) and super-Poissonian shot noise. This nontrivial behavior of tunnel magnetoresistance is associated with selection rules that govern tunneling processes and various high-spin states of the chain that are relevant for transport. For weak interdot correlations, on the other hand, the TMR is always positive and not larger than the Julliere TMR, although super-Poissonian shot noise and NDC can still be observed.