Spectroscopic evidence of two-impurity Kondo effect in potassium doped p-sexiphenyl films on Au (111)

Molecular magnetism is usually observed in organic coordination compounds consisting of transition metals or rare-earth metals, while it is rare in transition metal free or full-shell molecules. In this work, we grow high-quality p-sexiphenyl (PSP) monolayer film on Au (111) substrate, and then doped it with potassium (K) atoms. Various ordered phases are observed, with different structural and electronic properties. For a particular ordered phase, we observe obvious Kondo resonance peaks in isolated/misarranged PSP molecules, but clear splitting of such peaks is observed in PSP dimers. These phenomena share strong similarities to the two-impurity Kondo effect. Combined with theoretical calculation, we find that local spin is induced in PSP molecules by charge transfer from K atoms, leading to the appearance of Kondo resonance and the magnetic interaction of two Kondo impurities. Such two-impurity Kondo effect has only been reported in quantum dot system or dilute adatoms system, but the splitting of the Kondo resonance peak is much smaller than in our PSP system, which is as large as 5 meV. Our study not only provides a new and simple platform for investigating the two-impurity Kondo effect, but also provides a new route to construct a Kondo lattice on metal substrate.