Spin effects in single-electron tunnelling

Abstract

An important consequence of the discovery of giant magnetoresistance in metallic magneticmultilayers is a broad interest in spin-dependent effects in electronic transport throughmagnetic nanostructures. An example of such systems are tunnel junctions—single-barrierplanar junctions or more complex ones. In this review we present and discuss recenttheoretical results on electron and spin transport through ferromagnetic mesoscopicjunctions including two or more barriers. Such systems are also called ferromagneticsingle-electron transistors. We start from the situation when the central part of a devicehas the form of a magnetic (or nonmagnetic) metallic nanoparticle. Transportcharacteristics then reveal single-electron charging effects, including the Coulomb staircase,Coulomb blockade, and Coulomb oscillations. Single-electron ferromagnetic transistorsbased on semiconductor quantum dots and large molecules (especially carbon nanotubes)are also considered. The main emphasis is placed on the spin effects due to spin-dependenttunnelling through the barriers, which gives rise to spin accumulation and tunnelmagnetoresistance. Spin effects also occur in the current–voltage characteristics,(differential) conductance, shot noise, and others. Transport characteristics in the twolimiting situations of weak and strong coupling are of particular interest. In the former casewe distinguish between the sequential tunnelling and cotunnelling regimes. Inthe strong coupling regime we concentrate on the Kondo phenomenon, which inthe case of transport through quantum dots or molecules leads to an enhancedconductance and to a pronounced zero-bias Kondo peak in the differential conductance.