学术文献库

The effects of hole content (p) and oxygen deficiency (delta) on the zero-field critical current density, Jc0, were investigated for high-quality c-axis oriented Y1-xCaxBa2Cu3O7-delta (x = 0, 0.05, 0.10, and 0.20) thin films. Low temperature critical current density of these films above the optimum doping were found to be high and were primarily determined by the hole concentration, reaching a maximum at p ~ 0.185 +/- 0.005, irrespective of the level of oxygen deficiency. This implies that oxygen disorder plays only a secondary role and the intrinsic Jc0 is primarily governed by the carrier concentration in the copper oxide planes. Further support in favor of this was found from the analysis of the in-plane resistive transitions of c-axis oriented crystalline thin films of YBa2Cu3O7-delta (YBCO) under magnetic fields (H) applied along the c-direction, over a wide range of doped holes. The characteristic magnetic field (H0), linked to the vortex activation energy and the irreversibility field, exhibits similar p-dependence as shown by Jc0(p). We have explained these observations in terms of the doping dependent pseudogap (PG) in the low-energy electronic energy density of states. Both the intrinsic critical current density and the irreversibility field depend directly on the superconducting condensation energy, which in turn is largely controlled by the magnitude of the hole concentration dependent PG in the quasiparticle spectral density.