  We report unprecedented evidence of a spin split one-dimensional metallic
surface state for the system of Si(557)-Au obtained by means of high-resolution
spin- and angle-resolved photoelectron spectroscopy combined with first
principles calculations. The surface state shows double parabolic energy
dispersions along the Au chain structure together with a reversal of the spin
polarization with respect to the time-reversal symmetry point as is
characteristic from the Rashba effect. Moreover, we have observed a
considerably large out-of-plane spin polarization which we attribute to the
highly anisotropic wave function of the gold chains.
