Raman Scattering from Spin — Density Fluctuations in n — Ga As

Abstract

The anomalously large cross sections observed for scattering from single-electron excitations in GaAs can be explained in part as scattering from spin-density fluctuations. The electromagnetic field is coupled to the spins through second-order p∙ A perturbation terms involving the spin-orbit splitting of the valence band. At high carrier densities, where the screening wave vector is much greater than the momentum transfer, the spindensity fluctuations are not screened out as the charge-density fluctuations are, and hence the cross section can be much larger than that due to charge-density fluctuations alone. The polarization properties of the scattered radiation are also different for the two processes. For spin-density scattering the matrix element is proportional to \(\overrightarrow {\sigma \cdot } {\mkern 1mu} \left( {{{\hat \in }_1} \times {{\hat \in }_2}} \right),\) whereas for charge-density scattering it varies as \(\left( {{{\hat \in }_1}\cdot {{\hat \in }_2}} \right),\) where \({\hat \in _1}\) and \({\hat \in _2}\) are the incident and scattered polarization vectors. The magnetic field is taken to be zero throughout.