Energy-dependent broadening of Rashba-type spin splitting in a Au₂Sb surface alloy with periodic structural defects

Here, we report a novel two-dimensional (2D) Au ₂ Sb superstructure on Au(111) that exhibits both consistencies and discrepancies with the expected electronic features of an ideal 2D surface alloy with \(\:\sqrt{3}\times\:\sqrt{3}\) periodicity. Using spin- and angle-resolved photoemission spectroscopy, we observe a spin splitting of the alloy bands with antiparallel spin polarization, stemming from Rashba spin-orbit coupling. Notably, the Rashba bands are significantly broadened in comparison to idealized expectations. Taking advantage of the good agreement between the experimental results and DFT calculations, we identify the broadening of the Rashba bands as a consequence of perturbations introduced by three-pointed-star-shaped defects, which act as nonresonant impurities within the Au₂Sb superstructure. These periodic defects are capable of shifting the energy position of the Rashba bands without breaking the in-plane rotational and mirror symmetries, which suggests that the deliberate introduction of periodic defects into a Rashba SOC system possesses great potential in engineering the spin-dependent properties of spintronic devices.