Interplay between structural, chemical, and spectroscopic properties of Ag/Au(111) epitaxial ultrathin films: A way to tune the Rashba coupling

An overview of structural, chemical, and electronic properties of epitaxial Ag/Au(111) ultrathin films investigated by scanning tunneling microscopy and scanning tunneling spectroscopy and angle-resolved photoelectron spectroscopy is presented. New insights are exhibited: (i) a short-range ordered surface reconstruction is clearly observed for deposition at 300 K; (ii) self-organized ordering of Ag islands is obtained at T similar or equal to 80 K. In this whole temperature range, the Ag/Au(111) interface is shown to be (nearly) abrupt. An annealing of the elaborated room temperature leads to a strong intermixing and favors the formation of a chemically disordered surface alloy. The Shockley state parameters have been fully characterized for both interfaces. Surprisingly, the Rashba parameter is shown to scale the binding energy of the surface state in both cases. A simple one-dimensional model, taking into account the exponential decrease of the surface state wave function, allows us a quantitative understanding of the evolution of the surface state parameters. Indeed, the strength of the spin-orbit splitting is shown to be proportional to the number of heavy atoms probed by the surface state wave function, revealing its atomic character. Therefore, the strength of the Rasba coupling is shown to be tuned by adjusting the number of Ag epitaxial layers or the Ag-Au alloy composition.