Figure 4: Topology of linear band crossings.

(a) Sketch of spin-locked surface state near the point with Dirac point at E_D = 1.25 eV. Horizontal planes indicate calculated constant energy slices at E_D, and E_D ± 0.1 eV. The perpendicular plane displays the linear E (k_x = 0, k_y) dispersion with opposite spin orientation. (b,c) similar data near the Dirac point at (k_x = 0.40 Å⁻¹, k_y = 0.0 Å⁻¹, E_D = 0.84 eV) and the linear band crossing at (k_x = 0.80 Å⁻¹, k_y = 0.0 Å⁻¹, E_D = 0.84 eV). Blue and red colors represent directions of in-plane spin orientation extracted from the experimental and theoretical data shown in Fig. 1(e–h,j) and in Fig. 2 (second and fourth columns).