Anomalous Rashba effect of bismuth(111) thin films studied by high-resolution spin- and angle-resolved photoemission spectroscopy

The authors have developed an ultrahigh-resolution spin-resolved photoemission spectrometer equipped with a highly efficient mini Mott detector and a high-intensity xenon plasma discharge lamp. An electron deflector situated between the hemispherical electron-energy analyzer and the Mott detector enables the determination of the electron's spin-polarization in three independent directions and the spectrometer achieves an energy resolution of 0.9 and 8 meV for nonspin-resolved and spin-resolved modes, respectively. By using this spectrometer, we have performed spin- and angle-resolved photoemission spectroscopy of bismuth thin films on Si(111) to investigate the spin structure of surface states. Unlike conventional Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric across the zone center between the two elongated surface hole pockets and there is a giant out-of-plane spin polarization. The authors discuss these unusual spin textures in terms of a possible time-reversal symmetry breaking.