Dirac-cone-like surface state in W(110): dispersion, spin texture and photoemission from first principles

Abstract

We report on a theoretical study of a d _z ^2_2 surface state at the tungsten (110) surface, addressing in detail the spin-resolved electronic structure as well as photoemission spectroscopy. In agreement with recent experiments, this surface state shows a strongly anisotropic dispersion: in the $\overline{\mathrm{H}}$ – $\overline{\Gamma }$ – $\overline {\mathrm {H}}$ direction of the surface Brillouin zone, it disperses linearly but becomes flattened along the $\overline {\mathrm {N}}$ – $\overline {\Gamma }$ – $\overline {\mathrm {N}}$ direction. The ab initio calculated spin texture agrees with the one derived from a model Hamiltonian; due to twofold surface symmetry and time-reversal symmetry, the out-of-plane spin polarization vanishes. The photoemission intensities depend sensitively on the polarization of the incident light, because of the orbital composition of the surface state. The photoelectrons become spin-polarized out-of-plane, which is attributed to breaking the time-reversal symmetry by the excitation process.