Kondo effect of magnetic impurities in nanotubes.

Transition metal impurities will yield zero-bias anomalies in the conductance of well contacted metallic carbon nanotubes, but Kondo temperatures and geometry dependences have not been anticipated so far. Applying the density functional plus numerical renormalization group approach of Lucignano et al. to Co and Fe impurities in (4,4) and (8,8) nanotubes, we discover a huge difference of behavior between outside versus inside adsorption of the impurity. The predicted Kondo temperatures and zero-bias anomalies, tiny outside the nanotube, turn large and strongly radius dependent inside, owing to a change of symmetry of the magnetic orbital. Observation of this Kondo effect should open the way to a host of future experiments.