Magnetically induced spin relaxation in InAs QDs

The circular polarization $P$ of light emitted by Fe/InAs QDs spin LEDs has been studied as function of magnetic field $B $and temperature $T$. $P $shows a pronounced decrease around $B_{o }$= 5 T, in the form of a resonance with a full width of $\approx $ 0.75 T with the following characteristics: (i) The resonance strength is quite sensitive to the bias voltage $V$. At low $V $ the resonance is strong, but, as $V$ is increased, it becomes progressively weaker. (ii) The resonance is pronounced at $T$ = 5 K but loses strength with increasing temperature, and disappears above 60 K. The decrease in $P$ around $B_{o }$ is attributed to a spin relaxation mechanism that is induced by magnetic field. The sensitivity of the resonance to $V$ suggests that the origin of the spin relaxation mechanism is connected to the spin-orbit interaction. By changing $B$ we tune the energies of different electron states and thereby change the rate of spin relaxation in the system. We compare experimental results with calculations, in which many-body energies and wave functions are obtained using the effective-mass configuration-interaction approach; the spin-orbit interaction, is treated perturbatively. Work at SUNY was supported by ONR and NSF.