Superconducting condensate density of (La1−xCax)(Ba1.75−xLa0.25+x)Cu3O7+δ polycrystals

The superconducting condensate density ns of single-phase tetragonal (La1−xCax)(Ba1.75−xLa0.25+x)Cu3O7+δ polycrystals was examined by the magnetic measurements. The samples were synthesized with the composition range 0.1⩽x⩽1.0 by the amorphous metal-complex method. The magnetization curves were measured by a SQUID magnetometer. The lower critical field Hc1 was obtained from the magnetization curve using the modified Kim–Anderson critical-state model, in which Hc1 was taken into consideration. We estimated ns at 0 K from the temperature dependence of Hc1. The ns value increases until x=0.5 and decreases over x=0.5 as x increases. Besides, ns was found to be linear to the hole density. The present relation between the transition temperature Tc and ns is compared with the results for the underdoped samples by means of muon spin relaxation.