Oscillatory changes in the tunneling magnetoresistance effect in semiconductor quantum-dot spin valves

We experimentally study the tunneling magnetoresistance (TMR) effect as a function of bias voltage (V-SD) in lateral Ni/InAs/Ni quantum-dot (QD) spin valves showing Coulomb blockade characteristics. With varying V-SD, the TMR value oscillates and the oscillation period corresponds to conductance changes observed in the current-voltage (I-V-SD) characteristics. We also find an inverse TMR effect near V-SD values where negative differential conductance is observed. A possible mechanism of the TMR oscillation is discussed in terms of spin accumulation on the QD and spin-dependent transport properties via excited states.