Spin relaxation anisotropy: microscopic mechanisms for 2D systems

Low symmetry of two-dimensional (2D) semiconductor systems results in a dependence of the spin relaxation times on the spin orientation relative to crystallographic directions. It is demonstrated that a microscopic reason for this anisotropy is an interference of structure inversion asymmetry (SIA) and bulk inversion asymmetry (BIA). For the D'yakonov-Perel' spin relaxation mechanism the anisotropy is due to SIA and BIA interference in the spin splitting of energy spectrum. In the case of the Elliott-Yafet mechanism the spin relaxation anisotropy is caused by the interference of SIA and BIA in the spin-flip scattering probability.