The role of adsorption sites in the molecular kondo effect

We report on the observation of the Kondo effect for single iron phthalocyanine (FePc) magnetic molecules on an Au(111) surface using low temperature scanning tunneling microscopy. Two different Fano resonances induced by the Kondo effect have been observed experimentally. Through theoretical simulation and analysis we find that these two resonances correspond to different molecular adsorption sites. Adsorption sites play an important role both in the line shape of Fano resonances and in the strength of the spin-electron coupling. This provides an effective and practical method for tuning the spin-related properties of magnetic impurities on metal surfaces.