  Here, we report a novel AuSb 2D superstructure on Au(111) that shows
agreements and discrepancies to the expected electronic features of the ideal
2D surface alloys with $\sqrt{3}\times\sqrt{3}$ periodicity. Using spin- and
angle-resolved photoemission spectroscopy, we find a spin splitting of the
alloy bands with antiparallel spin polarization, stemming from Rashba
spin-orbit coupling. However, the observed Rashba bands are significantly
broadened. Taking advantage of the good agreement between the experimental
results and DFT calculations, we determine that the broadening of the Rashba
band is due to the perturbations from the 3-pointed-star-shaped defects acting
as nonresonant impurities in the Au2Sb superstructure. These periodic defects
can shift the energy position of the Rashba band without breaking the in-plane
rotational symmetry and mirror symmetry, which suggests that introducing
periodic defects into a Rashba SOC system possesses a great potential in
engineering the spin-dependent properties of spintronic devices.
