Spin-sensitive intersubband dynamics of optically generated carriers in semiconductor quantum wells

Abstract

A theoretical analysis of the intersubband dynamics in undoped quantum wells is presented where spin-oriented carriers are initially generated by circularly polarized interband excitations. Subsequent resonant intersubband excitations induce Rabi rotations between the subbands resulting in a fast periodic modulation of the spin orientation in each subband. It is investigated whether pure spin modulations can be performed where the charge density of the subbands is kept constant when initially equal occupations of the two lowest conduction subbands with opposite spin orientations have been prepared. While this is the expected behavior for a three-band model of noninteracting particles it turns out that when the Coulomb interaction is taken into account the spin modulations are typically accompanied by corresponding modulations of the subband occupations. It is demonstrated that under realistic conditions it should nevertheless be feasible to realize a pure spin rotation in a given subband provided the intersubband excitations are sufficiently short or the carrier density is sufficiently low. Successive spin rotations are shown to decrease the degree of spin polarization even when spin-relaxation processes are neglected.