Kondo effect by controlled cleavage of a single-molecule contact.

Conductance measurements of a molecular wire, contacted between an epitaxial molecule-metal bond and the tip of a scanning tunnelling microscope, are reported. Controlled retraction of the tip gradually de-hybridizes the molecule from the metal substrate. This tunes the wire into the Kondo regime in which the renormalized molecular transport orbital serves as a spin impurity at half-filling and the Kondo resonance opens up an additional transport channel. Numerical renormalization group simulations suggest this type of behaviour to be generic for a common class of metal-molecule bonds. The results demonstrate a new approach to single-molecule experiments with atomic-scale contact control and prepare the way for the ab initio simulation of many-body transport through single-molecule junctions.