Abstract

We discuss the significance of spin-relaxation for exciton dephasing in quantum well systems at low temperatures and also study the magnetic field dependence of spin-relaxation. We have used a novel technique employing reflective probing of pump-induced transient linear birefringence to investigate ultrafast dephasing of n=1 heavy-hole excitons as a function of magnetic field in GaAs/AlGaAs samples. We have also measured the spin-relaxation time and exciton lifetime of the samples. Exciton spin-relaxation in such samples is dominated, in zero field, by simultaneous electron and hole spin flips driven by confinement-enhanced exchange interaction [1]. We find that for localised excitons in narrow wells pure dephasing processes are negligible and spin-relaxation is dominant in zero magnetic field. In applied field the exciton spin-relaxation is strongly suppressed and the dephasing becomes lifetime-limited.

© 1996 Optical Society of America