Transport through two-level quantum dots weakly coupled to ferromagnetic leads

TL;DR

This paper theoretically investigates spin-dependent electron transport in a two-level quantum dot system with ferromagnetic leads, revealing how various regimes affect current, noise, and spin blockade phenomena.

Contribution

It introduces a detailed analysis of transport regimes in quantum dots with ferromagnetic leads, highlighting effects like negative differential conductance and spin blockade.

Findings

Current and noise depend strongly on transport regime.

Negative differential conductance can occur with asymmetric lead coupling.

Pauli spin blockade effects are observed with half-metallic and nonmagnetic leads.

Abstract

Spin-dependent transport through a two-level quantum dot in the sequential tunneling regime is analyzed theoretically by means of a real-time diagrammatic technique. It is shown that the current, tunnel magnetoresistance, and shot noise (Fano factor) strongly depend on the transport regime, providing a detailed information on the electronic structure of quantum dots and their coupling to external leads. When the dot is asymmetrically coupled to the leads, a negative differential conductance may occur in certain bias regions, which is associated with a super-Poissonian shot noise. In the case of a quantum dot coupled to one half-metallic and one nonmagnetic lead, one finds characteristic Pauli spin blockade effects. Transport may be also suppressed when the dot levels are coupled to the leads with different coupling strengths. The influence of an external magnetic field on transport properties is also discussed.