authors: Andrew Ho and Michele Fabrizio
Motivated by the appearance of superconductivity at the metal to a singlet Mott insulator transition in a three-band Hubbard model with inverted Hund's rules coupling recently discovered by Capone et al.(Science 296, p.2364 (2002)), we study the simplest single impurity analogue of that model. This is a two-orbital single impurity Anderson model with an "inverted Hund's rule" coupling K favouring a two-electron singlet ground state of the impurity. We analyse this model in the Kondo regime where valence fluctuations around the mean number n=2 of impurity electrons are suppressed. We find an unstable critical point as a function of K, which has the same form as in the two-impurity Kondo model (non-Fermi Liquid) critical point. At the critical point, there are enhanced superconducting fluctuations.