Giant Out-of-Plane Spin Component and the Asymmetry of Spin Polarization in Surface Rashba States of Bismuth Thin Film

We have performed high-resolution spin-and angle-resolved photoemission spectroscopy of bismuth thin film on Si(111) to investigate the spin structure of surface states. Unlike the conventional Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric between the two elongated surface hole pockets across the zone center. Moreover, we uncovered a giant out-of-plane spin polarization as large as the in-plane counterpart which switches the sign across the (Gamma) over bar-(M) over bar line. We discuss the present finding in terms of the symmetry breaking and the many-body effects.