Spin texture with a twist in momentum space for Tl/Si(111)

The electronic structure and spin texture around the $\overline{\mathrm{M}}$ point of $\mathrm{Tl}/\mathrm{Si}\left(111\right)\text{−}(1\times 1)$ is investigated with spin- and angle-resolved inverse photoemission and density-functional theory. The $\mathrm{Tl}/\mathrm{Si}\left(111\right)\text{−}(1\times 1)$ surface exhibits a surface-derived unoccupied state, which extends over the complete surface Brillouin zone. It is known for its giant spin-orbit-induced splitting and unique symmetry- and spin-orbit-induced spin landscape: a rotating spin pattern in momentum space along $\overline{\mathrm{\Gamma }}\overline{\mathrm{K}}$ and pure in-plane spin polarization along $\overline{\mathrm{\Gamma }}\overline{\mathrm{M}}$. Our results demonstrate how the $\overline{\mathrm{M}}$ point is encircled by this state. Its spin texture shows a peculiar twist, which reflects the $C_{1h}$ symmetry of the $\overline{\mathrm{M}}$ point.