Magnetization measurements of single-crystal Pb2Sr2(Y,Ca)Cu3O8: Determination of the coherence length and upper critical field

Magnetization measurements of single-crystal Pb2Sr2(Y,Ca)Cu3O8 from 5 to 250 K in a field of 1.5 T show that, with the field oriented perpendicular to the c axis of the crystal, there is a sharply defined onset of diamagnetism at Tc while with the field parallel to the c axis, the transition is rounded and the diamagnetism present above Tc as a result of superconducting fluctuations. The three-dimensional critical region just above Tc is found …