STRONG LOW-FIELD HC2 ANISOTROPY IN TL2BA2CA2CU3OX

Low-field dc magnetization measurements in fields between 0.5 and 40 G are reported on a single crystal of nominal composition Tl2Ba 2Ca2Cu3O10. It is observed that Hc2, determined from the diamagnetic onset temperature, is quite anisotropic. Extrapolating Hc2 to zero field yields zero field superconductive transition temperatures of Tc=118 K for H parallel to the c axis and Tc=111 K for H perpendicular to the c axis. This apparent inconsistency is thought to be due to the variation in stacking sequence of the Cu-O sheets.