Dark states in spin-polarized transport through triple quantum dot molecules

TL;DR

This paper investigates how dark states influence spin-polarized transport in triple quantum dot molecules, revealing complex behaviors like negative tunnel magnetoresistance and super-Poissonian shot noise due to quantum coherence and cotunneling effects.

Contribution

It provides a detailed analysis of dark states' impact on transport properties, highlighting the interplay of coherent trapping and cotunneling in spin-dependent quantum dot systems.

Findings

Negative tunnel magnetoresistance observed.

Super-Poissonian shot noise in dark state regimes.

Spin-dependent tunneling enhances noise effects.

Abstract

We study the spin-polarized transport through a triple quantum dot molecule weakly coupled to ferromagnetic leads. The analysis is performed by means of the real-time diagrammatic technique including up to the second order of perturbation expansion with respect to the tunnel coupling. The emphasis is put on the impact of dark states on spin-resolved transport characteristics. It is shown that the interplay of coherent population trapping and cotunneling processes results in a highly nontrivial behavior of the tunnel magnetoresistance, which can take negative values. Moreover, a super-Poissonian shot noise is found in transport regimes where the current is blocked by the formation of dark states, which can be additionally enhanced by spin-dependence of tunneling processes, depending on magnetic configuration of the device. The mechanisms leading to those effects are thoroughly discussed.