Spin-Polarized Dirac-Cone-Like Surface State with $d$ Character at W(110)

The surface of W(110) exhibits a Dirac-cone-like state with $d$ character within a spin-orbit-induced symmetry gap. As a function of the wave vector parallel to the surface, it shows a nearly massless energy dispersion and a pronounced spin polarization, which is antisymmetric with respect to the Brillouin zone center. In addition, the observed constant energy contours are strongly anisotropic for all energies. This discovery opens new pathways to the study of surface spin-density waves arising from a strong Fermi surface nesting as well as $d$-electron-based topological properties.

Figure 1

(a) Schematic illustration of experimental geometries for ARPES using synchrotron radiation (left) and spin-resolved ARPES using a He-discharge lamp (right). (b),(c) Energy-band dispersion curves of W(110) along $\overline{\Gamma S}$ measured with $p$-polarized synchrotron radiation light of $h\nu =22.5$ and 43 eV. (d) Magnified ARPES energy dispersion curve with enhanced momentum resolution for the crossing point of $S_1$. (e) Intensity maxima plot for one branch of $S_1$ obtained from momentum and energy distribution curves in (d). The hatched area shows the bulk continuum states outside the symmetry gap.

Figure 2

(a),(b) Spin-resolved EDCs of W(110) for positive and negative emission angles along the $\overline{\Gamma S}$ line excited with unpolarized $\mathrm{He}\mathrm{\text{−}}{I}_{\alpha }$ light ($h\nu =21.2\mathrm{eV}$). Spin-up and spin-down intensities are marked with triangles pointing up (red) and down (blue). (c) ARPES results obtained by $p$-polarized synchrotron radiation light ($h\nu =22.5\mathrm{eV}$). The contour plot is superimposed by triangles pointing up and down indicating the spin character of the corresponding spectral features, as derived from spin-resolved spectra in (a) and (b). Here, the non-spin-polarized peaks are denoted by squares (black). (d) Schematic $E$ vs $k_{\parallel }$ dispersion of $S_1$ and $B$ states without and with spin-selective hybridization.

Figure 3

ARPES results obtained with $p$-polarized synchrotron radiation light ($h\nu =43\mathrm{eV}$). (a),(b) Energy dispersion curves along $\overline{\Gamma S}$ and $\overline{\Gamma H}$. (c) Constant energy contours at several energies from 0 to 300 meV above the crossing point. (d)–(f) Selected constant energy contours at 300, 200, and 100 meV.