Radial spin helix in two-dimensional electron systems with Rashba spin-orbit coupling

We suggest a new long-lived spin-polarization structure, a radial spin helix [1], and study its relaxation dynamics. For this purpose, starting with a system of equations for spin-polarization density, we find its general solution in the axially symmetric case. It is demonstrated that the radial spin helix of a certain period relaxes slower than homogeneous spin polarization and plain spin helix [2]. Importantly, the spin polarization at the center of the radial spin helix stays almost unchanged at short times. At longer times, when the initial nonexponential relaxation region ends, the relaxation of the radial spin helix occurs with the same time constant as that describing the relaxation of the plain spin helix. Experimentally, such a structure can be created using spin injection or extraction in a system with cylindrical electrodes or, possibly, by a modified spin gratings technique. \\[4pt] [1] Y. V. Pershin and V. A. Slipko, Phys. Rev. B 82, 125325 (2010).\\[0pt] [2] Y. V. Pershin, Phys. Rev. B 71, 155317 (2005).