Figure 5: Spin texture of the topologically non-trivial surface state.

(a) Constant binding energy surface with a photon energy of 16 eV highlighting the surface state with linear dispersion. (b) In-plane ARPES dispersion along the direction emphasizing the position of the surface state with linear dispersion and the lower Rashba-like surface state. (c) Schematic FS diagram depicting the location of energy distribution curves (EDCs) 1–3. (d) Schematic in-plane ARPES dispersion with the measured in-plane spin-polarization marked. The surface state with linear dispersion shows strongly opposing polarizations on either side. Furthermore, the spin polarization for Rashba-like surface state alternates as expected. (e–g) EDCs and spin polarizations for the noted locations. Measured intensities are shown for the in-plane and out-of-plane spin EDCs. For in-plane spin polarization, positive (blue) spin polarizations correspond to polarization towards positive k_x, negative (red) spin polarizations correspond to polarization towards negative k_x. For out-of-plane spin polarization, positive (blue) spin polarizations correspond to polarization towards positive k_z, negative (red) spin polarizations correspond to polarization towards negative k_z. Consequently, considering EDCs 1–3 we note the presence of a anticlockwise helical spin texture with minimal radial component. Error bars are correspond to the statistical error from counting statistics (further discussion in Supplementary Note 4).