Spin coherence of holes and electrons in undoped CdTe/(Cd,Mg)Te quantum wells

The coherent spin dynamics of electrons and holes in an undoped CdTe/(Cd,Mg)Te quantum well structure was studied by time-resolved pump-probe Kerr rotation technique using resonant excitation of the charged exciton (trion) state. Long-living spin coherence of electrons (up to 10 ns) and holes (up to 500 ps) was measured. The unusual observation of long-living spin beats from both types of carriers in parallel is explained by coexistence of resident electrons and holes which are separated spatially in the quantum well plane. This conclusion is confirmed by experiments where type and concentration of resident carriers are tuned by above-barrier illumination.