Estimation of Cooper pair density and its relation to the critical current density in Y(Ca)BCO high-Tc cuprate superconductors

Abstract

Hole concentration (p) in the CuO2 plane largely controls all the electronic properties in the normal and superconducting states of high-Tc cuprates. The critical current density, Jc, is no exception. Previous hole content dependent studies have demonstrated the role of intrinsic depairing current density in determining the observed critical current density in copper oxide superconductors. The intrinsic pinning energy depends directly on the superconducting condensation energy which determines the magnitude of the depairing critical current density. Superconducting condensation energy is proportional to the Cooper pair density (superpair density) and depends strongly on the hole concentration within the CuO2 plane. We have calculated the Cooper pair density, ρs, of YBCO (Y123), a typical hole doped cuprate, as a function of p, in this study. A triangular pseudogap, pinned at the Fermi level, in the quasiparticle spectral density has been considered. The low-temperature zero-field critical current density of a number of high quality Y(Ca)BCO thin films over wide range of compositions and hole concentrations have been explored. The normalized values of the superpair density and the experimental critical current density exhibit a clear correspondence as the in-plane hole content is varied. This systematic behavior provides us with strong evidence that the critical current density of hole doped cuprates is primarily dependent on the superpair density, which in turn depends on the magnitude of the pseudogap energy. The agreement between the estimated p-dependent superpair density and the previously experimentally determined superfluid density of Y(Ca)BCO is quite good.