Spin effects in single electron tunneling

TL;DR

This review discusses recent theoretical advances in spin-dependent electron transport through ferromagnetic nanostructures, highlighting effects like spin accumulation, tunnel magnetoresistance, Coulomb phenomena, and the Kondo effect in various single-electron devices.

Contribution

It provides a comprehensive overview of theoretical results on spin effects in ferromagnetic mesoscopic junctions, including new insights into Coulomb and Kondo phenomena in these systems.

Findings

Spin accumulation and tunnel magnetoresistance are key effects in ferromagnetic tunnel junctions.

Coulomb blockade and Coulomb oscillations influence transport in single-electron transistors.

The Kondo effect enhances conductance and produces a zero-bias peak in quantum dot systems.

Abstract

An important consequence of the discovery of giant magnetoresistance in metallic magnetic multilayers is a broad interest in spin dependent effects in electronic transport through magnetic nanostructures. An example of such systems are tunnel junctions -- single-barrier planar junctions or more complex ones. In this review we present and discuss recent theoretical results on electron and spin transport through ferromagnetic mesoscopic junctions including two or more barriers. Such systems are also called ferromagnetic single-electron transistors. We start from the situation when the central part of a device has the form of a magnetic (or nonmagnetic) metallic nanoparticle. Transport characteristics reveal then single-electron charging effects, including the Coulomb staircase, Coulomb blockade, and Coulomb oscillations. Single-electron ferromagnetic transistors based 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-dependent tunnelling through the barriers, which gives rise to spin accumulation and tunnel magnetoresistance. Spin effects also occur in the current-voltage characteristics, (differential) conductance, shot noise, and others. Transport characteristics in the two limiting situations of weak and strong coupling are of particular interest. In the former case we distinguish between the sequential tunnelling and cotunneling regimes. In the strong coupling regime we concentrate on the Kondo phenomenon, which in the case of transport through quantum dots or molecules leads to an enhanced conductance and to a pronounced zero-bias Kondo peak in the differential conductance.