Low-temperature critical current of Y1−xCaxBa2Cu3O7−δ thin films as a function of hole content and oxygen deficiency

The effects of hole content (p) and oxygen deficiency (δ) on the zero-field critical current density, Jc0, were investigated for high-quality c-axis oriented Y1−xCaxBa2Cu3O7−δ (x = 0, 0.05, 0.10, and 0.20) thin films. Ca was used to introduce hole carriers in the CuO2 planes, independent of the oxygen deficiency in the CuO1−δ chains. Low-temperature Jc0 (16 K) of these films above the optimum doping were found to be high (>107 A/cm2) and were primarily determined by the hole concentration, reaching a maximum at p ∼ 0.185 ± 0.005, irrespective of oxygen deficiency. This implies that oxygen disorder plays only a secondary role and the intrinsic Jc0 is mainly governed by the carrier concentration and consequently by the superconducting condensation energy which also peaks at p ∼ 0.19 where the pseudogap correlation vanishes.