Effect of magnetic field on recombination dynamics in random electron systems

The evolution of localized electron states with increasing magnetic field is studied using time-resolved photoluminescence in GaAs/AlGaAs short-period superlattices, in which electrons are localized due to quantum interference between electron waves multiply scattered by the short-range potential of a random interface roughness. The nature of electronic states, extended or localized, is fundamentally related to the rate of their recombination, which is determined by the exciton coherence volume. Localization reduces the volume of exciton coherence, thereby decreasing the recombination rate. Correspondingly, the recombination rate in insulating samples turned out to be much lower than in metallic ones. Moreover, in insulating samples, the recombination rate increased with increasing temperature and magnetic field, which was found consistent with the temperature and magnetic field dependences of the electrical resistance. The observed increase in the recombination rate is attributed to the break-down of the quantum interference, leading to delocalization.