Coupling Asymmetry Effect on the Coherent Spin Current Through a Ferromagnetic Lead/Quantum Dot/Ferromagnetic Lead System

The spin dependent transport through asymmetric double barrier magnetic tunnel junction system is theoretically studied, based on the non-equilibrium Green´s function obtained via the equation of motion method. In the system, a single energy level is considered in the semiconductor quantum dot, which is asymmetrically coupled to the left and the right leads. It is found that due to the asymmetric coupling, the threshold voltages for charge current I - V characteristics are different for positive and negative applied bias, so are the spin current I - V characteristics. Besides, it is also found that the direction of current flow also modifies the electron occupancy within the dot.