Thin line of a Rashba-type spin texture: Unoccupied surface resonance of Tl/Si(111) alongΓ¯M¯

Abstract

The Tl/Si(111)-$(1\ifmmode\times\else\texttimes\fi{}1)$ surface features outstanding properties with a unique spin pattern in momentum space. Along $\overline{\ensuremath{\Gamma}}\overline{K}$ $(\overline{\ensuremath{\Gamma}}{\overline{K}}^{\ensuremath{'}})$, surface states with rotating spin had been observed. Here, the focus is put on the unoccupied surface electronic structure along the $\overline{\ensuremath{\Gamma}}\overline{M}$ high-symmetry direction. Spin- and angle-resolved inverse-photoemission experiments with sensitivity to the in-plane and out-of-plane components of the spin-polarization vector are conducted with the help of our recently developed rotatable spin-polarized electron source (ROSE). In agreement with our theoretical findings, we identify a surface resonance with giant spin-orbit-induced spin splitting, which exhibits an exclusive Rashba-type spin texture, i.e., a pure in-plane spin polarization perpendicular to $\overline{\ensuremath{\Gamma}}\overline{M}$, in compliance with the mirror-plane symmetry of the $\overline{\ensuremath{\Gamma}}\overline{M}$ direction. Notably, for slight deviations from the high-symmetry line, this constraint is lifted and additional spin-polarization components emerge. This highlights the importance of a correct alignment of the experiment when investigating samples with spin textures that are more complex than in simple Rashba systems or in ferromagnets.