Spatially modulated interface states in a two-dimensional potential: Single-layer RbI on Ag(111)

Alkali halides are known to exhibit interface electronic states (IES) when deposited on metal surfaces with ultra-thin coverage. Here, we examine the IES formed by sub-monolayer RbI growth on Ag(111), which exhibits spatial variations in electronic structure in surprising contrast to the results previously obtained for other alkali halides. We find that this spatially dependent behavior can be qualitatively modeled by using a two-dimensional cosine potential commensurate with the moire superstructure, where the IES is constructed from the well-known analytical solutions to the Mathieu equation. Our results indicate this potential is more corrugated than for similar potentials reported for other alkali halides, a result of substrate-adlayer charge transfer interactions that are stronger for RbI. This two-dimensional effective potential leads to anisotropy in the effective electron mass, in surprising contrast to previous results for other alkali halides, which report a single isotropic mass.