Spin Current Characteristics in a Quantum Dot-Ferromagnetic Contacts Sandwich Structure

We present an accurate theoretical treatment of spin current transport in a ferromagnetic-quantum dot-ferromagnetic (FM-QD-FM) system. The current flowing through the system is spin-polarized due to the spin asymmetric density of states (DOS) in the FM region. In the FM contacts, the spin current is modeled by the conventional macroscopic analysis-spin-drift-diffusion (SDD) model based on the Boltzmann equations. However, in the QD region, the current needs to be treated under mesoscopic regime to account for the electron correlation and the dot-leads coupling. We use the Keldysh non-equilibrium Green function (NEGF) approach based on equation of motion technique to model the current transport in the dot region and integrate the macroscopic treatment in the FM leads and microscopic treatment in the QD in a self-consistent manner. The multi-scale approach we introduced here presents a realistic and simplified way for calculating spin current in such a FM-QD-FM system.