Conductance and Kondo effect in a controlled single-atom contact.

The tip of a low-temperature scanning tunneling microscope is brought into contact with individual cobalt atoms adsorbed on Cu(100). A smooth transition from the tunneling regime to contact occurs at a conductance of G approximately G0. Spectroscopy in the contact regime, i.e., at currents in a muA range, was achieved and indicated a significant change of the Kondo temperature TK. Calculations indicate that the proximity of the tip shifts the cobalt d band and thus affects TK.