Upper Critical Fields of Ba₂YCu₃O9-δ

The temperature dependence of the upper critical field H c2 of the high T c superconductor Ba 2 YCu 3 O 9-δ was measured resistively between 0 and 40 T on a single phased sample with T c =92 K. The critical field defined as the midpoint of the transition reaches 34 T at the boiling point of liquid-nitrogen. From the initial slope of the H c2 (T) curve of - 1.27 T/K, the electronic specific heat coefficient was estimated to be 7.5 mJ/mol·K 2 using the dirty limit approximation.