Direct observation of resonant tunneling dynamics in high magnetic fields

Magnetotunneling of electrons in an asymmetric double quantum well is investigated by time-resolved luminescence spectroscopy. The tunneling time decreases strongly when the bottom of the lowest electronic subband of the narrow well is brought to intersect the lowest wide well subband at nonzero wave vector by a magnetic field perpendicular to the growth direction. This decrease is particularly pronounced when longitudinal optical phonon emission is possible. Transfer becomes then as fast as in electrically tuned resonances in zero magnetic field.