Extended Data Fig. 6: Further evidence for the Dresselhaus-like in-plane spin texture.

a, DFT-calculated spin-resolved CEC at k_z = −0.2π/c and binding energy E_B = 0.45 eV. In-plane spins point mainly along ±S_x+y and ±S_x−y, resembling the Dresselhaus configuration. The direction of +S_x+y and +S_x−y are defined along k_x + k_y and k_x − k_y, respectively, shown in the bottom-left inset. The top-right inset depicts the schematic spin texture centred at point B. b, Spin-integrated ARPES band dispersion along Cut 5. Cuts 5 and 6 are defined in a; the bands along Cut 6 (not shown) seem the same. The observed bands exhibit two hole pockets and further intensity at k = 0 and E_B = 0.4 eV. c,d, S_x+y-resolved and S_x−y-resolved raw E–k cuts along Cuts 5 and 6. Blue/red circles highlight the regions with +/− polarizations. The SARPES results (i) vaguely corroborate with the DFT-calculated results (ii), which becomes more obvious by overlaying the calculated spin-resolved energy bands on the SARPES images (iii). iv, Polarization curves (top) and spin-integrated intensity curves (bottom) at k = ±0.18 Å⁻¹, integrated within the dashed rectangles in iii. Each point on a curve is an integrated intensity over a (E, k) range of (50 meV, 0.08 Å⁻¹). These spin-resolved EDCs reveal three important features. First, the S_x+y polarizations at k_x+y = ±0.18 Å⁻¹ have opposite polarizations at the same binding energy. Second, the polarization at low binding energy (about 0.25 eV) and high binding energy (about 0.55 eV) is opposite. The corresponding S_x−y polarization of Cut 6 also exhibits these two features. Third, comparing the polarization curves at −0.18 Å⁻¹ in Cuts 5 and 6, we find that their polarizations are opposite at the same binding energy. Extracted from the polarization curves, the energy scale of the spin splitting is about 274 ± 40 meV, which is in good agreement with the calculated 297 meV and is comparable with the well-known giant bulk Rashba effect³⁸. v, Polarization curves versus momentum. We can trace the splitting along k and find that the +S_x+y (−S_x−y) spin-polarized peaks of Cut 5 (Cut 6) move downward in energy when k moves away from O. In summary, our SARPES data along Cuts 5 and 6 reveal a Dresselhaus-like in-plane spin texture and ruled out a Rashba-like spin texture.