On the zero-bias anomaly in K-doped $C_{60}$ on Ag(100)

The fullerene molecule $C_{60}$ is known to undergo a strong Jahn-Teller distortion when electrons are added. Recent STM/STS experiments indicate that a single $C_{60}$ molecule on a Ag(100) surface can be controllably doped with charge-donating potassium atoms;~[1] moreover, the experiments suggest that the molecular electronic structure can be tuned so that a single electronic orbital lies near the Fermi level. Starting from a Hamiltonian with parameters inferred from companion density functional theory (DFT) calculations of $K_{x}C_{60}$ on Ag(100), we use Wilson's numerical renormalization group to compute the spectrum near the Fermi level of a doped $C_{60}$ molecule coupled to a metallic continuum. The result compares favorably with spectroscopic measurements of the zero-bias anomaly and, together with the DFT calculations, explains the electronic structure of this system over a range of dopings. \newline \newline [1] R. Yamachika, M. Grobis, A. Wachowiak, and M.F. Crommie, {\it Science} {\bf 304}, 281-284 (2004).