Flux quantization and diamagnetic currents in strongly correlated systems

Within the basic assumption that oxygen orbitals may play a fundamental role in the superconductive properties of Cu-O high-Tc materials, exact calculations of the ground-state energy and thermodynamic properties of strongly interacting fermions in small oxygen rings have been performed. Persistent currents (mesoscopic effect) and supercurrents have been computed for several microscopic models including repulsive and attractive Hubbard and the occupation-dependent hopping Hamiltonians. It is shown that for a given range of parameters the latter model exhibits features reminiscent of superconductivity: a maximum in the temperature dependence of the specific heat, whose position correlates with the temperature at which the superelectron concentration vanishes and exact hc/2e-periodic dependence of the free energy as a function of magnetic flux