Extreme magnetic modulation of the exciton transfer rate between unequal quantum wells

We show that a moderate in-plane magnetic field quenches the Stokes transfer of excitons between direct and indirect (i.e., type II) quantum wells at low temperatures. The transfer is due to the decay of an exciton in the initial well into a free electron-hole pair in the final well. Higher fields open, within a narrow range of field, a new dramatically enhanced resonant transfer channel for both the Stokes and the anti-Stokes transfer between the higher-energy direct and lower-energy indirect exciton states. The rates are calculated for ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ quantum wells.