Unveiling Pseudo-Dirac Resonances in the (√7x√7)R19.1° Phase of Sulfur Segregated on Cu(111) Surface

The Cu-S alloy is of great scientific importance due to its wide range of technological applications, including Cu-S antifluorite crystals exhibiting topological states. To gain insights into the sulfur-copper interaction, a simplified model of sulfur adsorption in copper is commonly used, particularly in surface reconstructions like the (root 7x root 7)R19.1 degrees phase. However, determining the optimal structural model for this type of reconstruction has been a persistent challenge. Among the various models proposed to explain the reconstruction, Foss and Prince models have gained greater acceptance. In our comprehensive study, we employed a comparative approach utilizing angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and density functional theory calculations. Our objective was to investigate the band structure and local density of states of this reconstruction resulting from sulfur segregation on the Cu(111) surface, with the aim of assessing the compatibility of the experimental results with the two leading models. Remarkably, our analysis unveiled intriguing localization effects within the bulk resonances and distinctive surface bands originating from the copper-sulfur cluster present in both models. Through careful examination of electronic dispersion and the local density of states, we successfully distinguished between the models and determined which one better aligned with our experimental data.