Rashba effect of bismuth thin film on silicon studied by spin-resolved ARPES

We report high-resolution spin- and angle-resolved photoemission spectroscopy of bismuth thin film on Si(1 1 1) to discuss the spin structure of surface states. We found that, unlike conventional picture of the Rashba splitting, the magnitude of the in-plane spin polarization is asymmetric between two hole pockets across the Brillouin-zone center. In addition, these pockets exhibit a giant out-of-plane spin polarization as large as the in-plane counterpart, which changes the sign across the Γ¯M¯ line. We also revealed that the spin polarization of the Rashba surface states near the Brillouin-zone boundary (the M¯ point) is gradually reduced on decreasing the film thickness. Our result provides a new pathway to generate and control spin-polarized electrons in the Rashba system.