Rotating spin and giant splitting: Unoccupied surface electronic structure of Tl/Si(111)

Stolwijk Sebastian D., Schmidt Anke B., Donath Markus , Sakamoto Kazuyuki , Krüger Peter

Abstract

We present a combined experimental and theoretical study on the unoccupied surface electronic structure of the Tl/Si(111) surface. Spin- and angle-resolved inverse-photoemission measurements with sensitivity to both the in-plane and the out-of-plane polarization direction detect a spin-orbit-split surface state, which is well described by theoretical calculations. We demonstrate that the spin polarization vector rotates from the classical in-plane Rashba polarization direction around Γ̄ to the direction perpendicular to the surface at the K̄(K̄′) points - a direct consequence of the symmetry of the 2D hexagonal system. A giant splitting in energy of about 0.6 eV is observed and attributed to the strong localization of the unoccupied surface state close to the heavy Tl atoms. This leads to completely out-of-plane spin-polarized valleys in the vicinity of the Fermi level. As the valley polarization is oppositely oriented at the K̄ and K ̄′ points, backscattering should be strongly suppressed in this system. © 2013 American Physical Society.