Unexpected behavior of diamagnetic signal in polycrystalline Bi2Sr2Ca1−xYxCu2O8+δ

The effect of superconductivity and inhomogeneity on the phase coherence between superconducting grains for Bi2Sr2CaCu2O8+δ (Bi-2212) is discussed. We find that in the UD regime, inhomogeneity plays a central role in establishing the phase coherence between superconducting grains. By decreasing hole concentration, p, the phase stiffness for the thermal fluctuations is suppressed, whereas the phase coherence between the superconducting grains is enhanced. In particular, the phase coherence between the superconducting grains is established almost immediately as the superconductivity for Bi-2212 with p ≃ 0.075 appears.