Superconductivity in mesoscopic high-Tc superconducting particles

Based on the Hubbard model in the framework of non-phonon kinematical mechanism and taking into account the discreetness of an electronic energy spectrum. the superconducting critical temperature of a mesoscopic high-T-c sphere is analyzed as a function of doping and as a function of particle's radius. The critical temperature T-c is found to be an oscillating function of the radius of a particle. The size-dependent doping regime is revealed in high-T-c nanoparticles. Our analysis shows that each oscillation in T-c corresponds to the increase in a number of the energy levels in the sphere by 1. The amplitude of oscillations of T-c increases with decreasing R and can reach a value of 6 K for nanoparticles with sizes about 25 nm, in good agreement with experimental studies of YBa2Cu3O7-delta nanoparticles. (C) 2003 Elsevier Science Ltd. All rights reserved.