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-Tc sphere is analyzed as a function of doping and as a function of particleʹs radius. The critical temperature Tc is found to be an oscillating function of the radius of a particle. The size-dependent doping regime is revealed in high-Tc nanoparticles. Our analysis shows that each oscillation in Tc corresponds to the increase in a number of the energy levels in the sphere by 1. The amplitude of oscillations of Tc 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−δ nanoparticles.