Infinite Spin Diffusion Length of Any Spin Polarization Along Direction Perpendicular to Effective Magnetic Field from Dresselhaus and Rashba Spin-Orbit Couplings with Identical Strengths in (001) GaAs Quantum Wells

In this note, we show that the latest spin grating measurement of spin helix by Koralek et al. (Nature 458: 610, 2009) provides strong evidence of the infinite spin diffusion length of any spin polarization along the direction perpendicular to the effective magnetic field from the Dresselhaus and Rashba spin-orbit couplings with identical strengths in (001) GaAs quantum wells, predicted by Cheng et al. (Phys. Rev. B 75: 205328, 2007).