Carrier spin dynamics in ${\mathrm{C}\mathrm{d}\mathrm{T}\mathrm{e}/\mathrm{C}\mathrm{d}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ quantum wells

We investigated the carrier spin dynamics in diluted magnetic semiconductor quantum wells, ${\mathrm{C}\mathrm{d}\mathrm{T}\mathrm{e}/\mathrm{C}\mathrm{d}}_{1-x}{\mathrm{Mn}}_x\mathrm{Te}$ $(x\approx 0.35),$ using femtosecond time-resolved circular dichroic spectroscopy. When the heavy-hole exciton was resonantly excited by the circularly polarized laser pulse, the positive and negative circular dichroism appeared at the heavy-hole– and the light-hole–exciton energy, respectively. They decay with different time constants, from which we succeeded in determining the spin dynamics of electrons separately from that of holes. Furthermore, we found that the electron-spin-relaxation time decreases dramatically with decreasing the well width, while the heavy-hole–spin relaxation is relatively insensitive to the variation of the well width. This strongly suggests that the electron-spin-relaxation process is governed by the $s-d$ exchange interaction in the magnetic barrier layer, while the heavy-hole–spin relaxation by $p-d$ exchange interaction is regulated by the degree of the mixing between the heavy- and light-hole subbands.