Magnetic impurities and Kondo conductance anomalies in nanotubes: the importance of being ``in''*

Transition metal impurities should yield zero bias anomalies in the conductance of well contacted metallic carbon nanotubes, but relevant temperatures and lineshapes cannot be anticipated without accurate ab initio calculations. Applying the density functional plus numerical renormalization group approach of Lucignano et al [1] to Co and Fe impurities in (4,4) and (8,8) nanotubes, we discover a huge difference of behaviour between outside versus inside impurity adsorption. The predicted Kondo temperatures and zero bias anomalies, tiny when the impurity is outside the nanotube [2] turn large and strongly radius dependent inside, owing to a change of symmetry of the magnetic orbital. These results foreshadow interesting field and temperature dependent nanotube electrical transport, to be addressed in future experiments.\\[4pt] [1] P. Lucignano, et al., Nature Materials 8, 563 (2009).\\[0pt] [2] P. Baruselli, et al., Physica E (2011) doi:10.1016/j.physe.2011.05.005