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Recent scanning tunneling microscope (STM) experimental studies on transport through CoPc and TBrPP-Co molecules adsorbed on metallic surfaces have reported several interesting results: (i) a high Kondo temperature as compared to those of adsorbed undressed magnetic atoms, (ii) the Kondo resonance shows up either as a Kondo peak (CoPc) or as a Fano dip (TBrPP-Co), (iii) the Kondo temperature depends strongly on the molecule conformation and can be manipulated experimentally. Aiming to propose a theoretical framework that may serve to analyze these observations, we first discuss the case of an isolated magnetic atom adsorbed on a metallic surface. Much of the work on this simple case turns out to be of great help in the analysis of the more complex systems. Then, a simple model is proposed that, capturing the main features of the inner structure of the molecule (four lobe orbitals plus a strongly correlated orbital), offers a physical interpretation for most of the observations on those two moecules. In addition, it allows predicting the behavior of the system upon other symmetry or conformational changes, or when the STM tip is moved away from the Co atom.

We analyze two possible confining potentials for nanoscopic rings. We compare here the displaced parabola (Hill) and the “centrifugal core” (Vulcan) confining potentials. The corresponding eigenvalues are analyzed as a function of ring radius and of an external magnetic field, perpendicular to the plane of the ring. An absolute minimum is found for the lowest eigenvalue of the Hill potential. The characteristic signatures of both potentials are displayed (for example, angular momentum level crossing), and thus the one that best fits the one-electron spectroscopic data can be chosen as a basis for the study of the many-body effects. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)