Direct observation of spin splitting in bismuth surface states

Abstract

The electronic structure of ultrathin Bi(001) films on $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ was studied by spin and angle-resolved photoemission spectroscopy. We directly observed a clear momentum-dependent spin splitting and polarization of the surface-state bands. The spin structure was antisymmetric with respect to the $\overline{\ensuremath{\Gamma}}$ point as predicted by theory, and the obtained in-plane spin polarization was as high as $\ifmmode\pm\else\textpm\fi{}0.5$. The qualitative features of the observed spin polarization are discussed in comparison with the spin-polarized band structure obtained by first-principles calculations.