Nonlinear Rashba Model and Spin Relaxation in Quantum Wells
  We find that the Rashba spin splitting is intrinsically a nonlinear function of the momentum, and the linear Rasha model may overestimate it significantly, especially in narrow-gap materials. A nonlinear Rashba model is proposed, which is in good agreement with the numerical results from the eight-band kp theory. Using this model, we find pronounced suppression of the D'yakonov-Perel' spin relaxation rate at large electron densities, and a non-monotonic dependence of the resonance peak position of electron spin lifetime on the electron density in [111]-oriented quantum wells, both in qualitative disagreement with the predictions of the linear Rashba model. 
W. Yang, Kai Chang