Spin Polarized Transport through the Double-Dot System

Abstract

Spin-polarized transport in nanoscopic systems was mainly investigated for a single quantum dot (QD) attached to ferromagnetic electrodes (see e.g. [1]). It was shown that such a set could act as a spin valve. The current flowing through QD strongly depends on the configuration of magnetic moments in the leads. Usually, it is maximal for configuration in which magnetic moments are parallel in both electrodes. Spin-based devices are very important due to possibility of their application in spintronics. Especially, double quantum dot (DQD) structures could probably work in quantum computer hardware [2]. Electron transport through a double dot system received much experimental and theoretical attention during the past decade [3, 4], however, systems with non-magnetic electrodes were mainly investigated. Recently, spin-dependent transport has been studied for a set of two quantum dots capacitively coupled [5]. The linear conductance in the Kondo regime has been mainly investigated. Here, we analyze spin-dependent transport through a system of two quantum dots in series. The inter-dot tunnel coupling can be easily tuned in such systems [6]. It strongly influences the current flowing through the system. Using the non-equilibrium Green function formalism based on the equation of motion we show that the DQD set can act as an effective spin valve in which not only tunnel magnetoresistance (TMR) value but also its sign can be easily changed with inter-dot coupling.