Kondo Temperature of Magnetic Impurities at Surfaces

Based on the experimental observation that only the close vicinity of a magnetic impurity at metal surfaces determines its Kondo behavior, we introduce a simple model which explains the Kondo temperatures observed for cobalt adatoms at the (111) and (100) surfaces of Cu, Ag, and Au. Excellent agreement between the model and scanning tunneling spectroscopy experiments is demonstrated. The Kondo temperature is shown to depend on the occupation of the $d$ level determined by the hybridization between the adatom and the substrate with a minimum around single occupancy.

Figure 1

Spectra taken on a cobalt adatom on Ag(100) as well as on cobalt adatoms on Ag(111), one monolayer of Ag on Cu(111), and on Cu(111). The solid lines depict the fit of a Fano line shape [Eq. (1)] to the data.

Figure 2

(a) Kondo temperature $T_K$ as a function of the occupation $n_d$ of the $d$ level calculated with Eqs. (3, 4, 5). (b) Shift of the Kondo resonance ${ϵ}_K$ with respect to the Fermi energy; the solid line shows the prediction by our model according to Eq. (6).