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

Abstract

Spin-dependent transport through a two-level quantum dot in the sequential tunnellingregime is analysed theoretically by means of a real-time diagrammatic technique. It isshown that the current, tunnel magnetoresistance, and shot noise (Fano factor) stronglydepend on the transport regime, providing detailed information on the electronic structureof quantum dots and their coupling to external leads. When the dot is asymmetricallycoupled to the leads, a negative differential conductance may occur in certain biasregions, which is associated with a super-Poissonian shot noise. In the case of aquantum dot coupled to one half-metallic and one nonmagnetic lead, one findscharacteristic Pauli spin blockade effects. Transport may also be suppressed whenthe dot levels are coupled to the leads with different coupling strengths. Theinfluence of an external magnetic field on transport properties is also discussed.