Figure 4: Spin character of the metallic band.

SARPES spectra measured along the k_y direction around (a) the point and (b) the point, and (c) along the k_x direction around the point. The directions of the wave vectors k_x and k_y are shown in Figure 3b. The red (blue) spectra represent the spin pointing to positive (negative) z as indicated in the inset. (d) Schematic illustration of the spin-polarized surface states at and . The green (purple) hexagon represents the SBZ. The position of the SBZ is here used to indicate the Fermi level at a coverage of 1.12 (1.01) ML. Illustrations of scattering processes (e) without and (f) with spin flipping. k_i is the wave vector of the incident electrons, and k₁ and k₂ are the wave vectors of the scattered ones. q₁ and q₂ (q₂′) are the intravalley and intervalley scattering wave vectors. (g) A 41.7 × 41.7 nm² STM image of a Si(111) surface with 1.01 ML of adsorbed Tl. V_sample and tunneling current are +1.0 V and 3.0 nA, respectively. (h) Two-dimensional FFT map of an STM topography obtained for a sample with <0.0005 ML of extra Tl at a V_sample of +0.25 V. The inset in h is the 30 × 30 nm² STM topography. q space maps of scattering amplitudes obtained from FFT of dI/dV maps at V_sample of (i) +0.5 V and (j) +0.25 V. The insets in i and j are the quasiparticle interference patterns of 30 × 30 nm² images.