LAUSR

Spin polarization by Rashba effect in the quasi-one-dimensional metallic bands of $\mathrm{Si}(111)5\ifmmode\times\else\texttimes\fi{}2$-Au surface is revealed by spin- and angle-resolved photoelectron spectroscopy and the first-principles calculation. Small but clear spin polarization and its sign reversal with respect to the $\overline{\mathrm{\ensuremath{\Gamma}}}$ point is observed indicating the Rashba origin of the spin-polarized states. Deviating from the typical helical tangential spin texture of normal Rashba effect of two-dimensional electronic states, not only in-plane but significant out-of-plane spin polarization probably caused by the anisotropic in-plane charge distribution around Au atoms is observed at some specific $k$ points. The observed peculiar spin texture of the sample is qualitatively in good agreement with the results of the first-principles calculation based on the recently proposed surface reconstruction model by Kwon and Kang implying the validity of the structural model.