Conductance and Kondo effect of a controlled single atom contact

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The tip of a low-temperature scanning tunneling microscope is brought into contact with individual Kondo impurities (cobalt atoms) adsorbed on a Cu(100) surface. A smooth transition from the tunneling regime to a point contact with a conductance of G₀ occurs. Spectroscopy in the contact regime, i. e., at currents in a μA range was achieved. A modified line shape is observed indicating a significant change of the Kondo temperature Tₖ at contact. Model calculations indicate that the proximity of the tip shifts the cobalt d-band and thus affects Tₖ.