Microscopic approach to spin dynamics: meaning of spin relaxation times

Abstract

We present an approach to spin dynamics by extending the optical Bloch equation s for the driven two-level system to derive microscopic expressions for the tra nsverse and longitudinal spin relaxation times. This is done for the 6-level sy stem of electron and hole subband states in a semiconductor or a semiconductor quantum structure to account for the degrees-of-freedom of the carrier spin and the polarization of the exciting light and includes the scattering between car riers and lattice vibrations on a microscopic level. For the subsystem of the s pin-split electron subbands we treat the electron-phonon interaction in second order and derive a set of equations of motion for the 2 x 2 spin-density matrix which describes the electron spin dynamics and contains microscopic exp ressions for the longitudinal (T) and the transverse (T) spin relaxatio n times. Their meaning will be discussed in relation to experimental investigat ions of these quantities.