COMPLEX SUSCEPTIBILITY AND CRITICAL CURRENT OF HIGH-TEMPERATURE SUPERCONDUCTORS

The ac complex susceptibility χ′−iχ″ of several bulk samples with very high critical current density J c have been measured. The results show that these samples are all polycrystalline bulk material, the peak of χ″ still related to losses within “the weak link structure” of the intergrain material. But the intergrain coupling strength of the high J c samples is much stronger than ordinary high-T c superconductors. A parameter β=(T c2 (0) −T c2 (h 0 ))/h 0 2/3 has been proposed to characterize the coupling strength.