Spin Dependent Resonant Tunneling

Resonant tunneling in double barrier tunnel junctions (DTJs) has been known in semiconductors, in which the quantum well (QW) states are formed in a layer with the discreet energy levels, when the intermediate layer thickness sandwiched by two barriers is thin enough. When the bias voltage is applied to the junction, QW states move down and the electrons can tunnel through the discreet energy level, namely the resonant tunneling occurs when the discreet energy level enters in the band of the electrode, and the tunnel current increases and takes the maximum when the energy level E0 reaches the bottom of the energy band of the electrode, after that decreases with increasing the voltage. The negative resistance is observed.

How about the double magnetic tunneling junctions (DMTJs) with a ferromagnetic metallic intermediate layer ? In this case QW states are spin dependent due to the exchange splitting of an intermediate ferromagnetic layer. So, the up- and down-spins resonantly tunnel at the different bias voltages, and so the tunnel conductance has the maximums at the different bias voltages for parallel and antiparallel magnetization configurations of the ferromagnetic layers. In this case we can expect the oscillation of the TMR as a function of the voltage and the enhancement of the TMR.