Observation of a Fano Resonance in Photoemission

Abstract

We report on the observation of a Fano resonance in normal emission ultraviolet photoelectron spectra of Cu or Ag impurities embedded in a Xe monolayer on highly oriented pyrolytic graphite. We show that Brillouin-zone folding resulting from the relatively weak perturbation by the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ commensurate Xe overlayer couples $K$-point electrons with $\ensuremath{\Gamma}$-point electrons of pure graphite. Interference between this continuum of states and the discrete Cu $4s$ or Ag $5s$ states in the initial state leads to a typical Fano line profile in the spectra. This finding provides a new and promising avenue for the detection and characterization of impurities or small clusters at surfaces.