Direct evidence of the contribution of surface states to the Kondo resonance

Abstract

Using low-temperature scanning tunneling microscopy/spectroscopy, the Kondo resonance was observed on an isolated 5, 10, 15, 20-tetrakis-(4-bromophenyl)-porphyrin-Co (TBrPP-Co) molecule adsorbed on the Si(111)-root 3 x root 3Ag substrate. As the substrate has a two-dimensional surface state and does not have bulk states around the Fermi level (E-F), the Fano-shaped peak near E-F observed above the molecule caging a spin-active cobalt atom is a direct evidence of the contribution of the surface-state electrons to the Kondo resonance. The long decay length (similar to 1.6 nm) of the resonance also supports for the surface-state contribution.