Spin dynamics in the second subband of a quasi–two-dimensional system studied in a single-barrier heterostructure by time-resolved Kerr rotation

Abstract

Spin dynamics in the first and second subbands have been examined simultaneously by time resolved Kerr rotation in a single-barrier heterostructure of a 500 nm thick GaAs absorption layer. By scanning the wavelengths of the probe and pump beams towards the short wavelength in the zero magnetic field, the spin coherent time T21* in the 1st subband E1 decreases in accordance with the D'yakonov-Perel' (DP) spin decoherence mechanism. Meanwhile, the spin coherence time T22* in the 2nd subband E2 remains very low at wavelengths longer than 810 nm, and then is dramatically enhanced afterwards. At 803 nm, T22*(450 ps) becomes ten times longer than T21*(50 ps). A new feature has been discovered at the wavelength of 811 nm under the bias of −0.3 V (807 nm under the bias of −0.6 V) that the spin coherence times (T21* and T22* ) and the effective g* factors (|g*(E1)| and |g*(E2)|) all display a sudden change, presumably due to the “resonant" spin exchange coupling between two spin opposite bands.