Kinetics of spin coherence of electrons in an undoped semiconductor quantum well

We study the kinetics of spin coherence of optically excited electrons in a n undoped insulating ZnSe/Zn1-xCdxSe quantum well under moderate magnetic f ields in the Voigt configuration. After clarifying the optical coherence an d the spin coherence, we build the kinetic Bloch equations and calculate de phasing and relaxation kinetics of laser pulse-excited plasma due to static ally screened Coulomb scattering and electron-hole spin exchange. We find t hat the Coulomb scattering cannot cause the spin dephasing, and that the el ectron-hole spin exchange is the main mechanism of the spin decoherence. Mo reover the beat frequency in the Faraday rotation angle is determined mainl y by the Zeeman splitting, redshifted by the Coulomb scattering and the ele ctron-hole spin exchange. Our numerical results are in agreement with exper imental findings. A possible scenario for the contribution of electron-hole spin exchange to the spin dephasing of the n-doped material is also propos ed.