Direct evidence of the surface state contribution to the Kondo resonance

We performed low temperature scanning tunneling microscopy/spectroscopy on the isolated single 5, 10, 15, 20-tetrakis-(4-bromophenyl)-porphyrin-Co (TBrPP-Co) molecules adsorbed on the Si(111)- $\sqrt 3 \times \sqrt 3 $ Ag substrate. On this substrate, all the TBrPP-Co molecules show a square shape, indicating a planar conformation with a spin-active Co atom caged at its center. As the substrate supports a two-dimensional surface state and does not have bulk state near the Fermi level, the observed Fano-shaped peak near the Fermi level taken above the single molecule is a direct evidence of the contribution of the surface state electrons to the Kondo resonance. The long decay length ($\sim $ 1.4 nm) of the resonance also support for the surface state contribution. [1] Q. Li, S. Yamazaki, T. Eguchi, Y. Hasegawa, H. Kim, S.-J. Kahng, J. F. Jia, and Q. K. Xue, Nanotechnology 19, 465707 (2008).