Josephson coupling between superconducting clusters in high-Tc materials

Abstract Diamagnetic moment for Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi:2212) and YBa 2 Cu 3 O 7− δ (Y:123) crystals were measured at different fields H and temperatures. For the higher fields two distinct transition temperatures T g and T J are identified, with T g > T J . By increasing H the line T g ( H ) shifts very slowly while T J ( H ) shifts much faster to lower temperatures, displaying an upward curvature well described by a theory based on Josephson coupling between superconducting clusters. Here, we show data mainly for the Bi:2212 crystals, where sample dependent T J ( H ) lines are clearly observed.