Upper Critical Field of High Tc Superconductor Y0.4Ba0.6CuO2.22

The upper critical field of Y0.4Ba0.6CuO2.22 has been studied by the electrical resistivity measurement in the magnetic field up to 23.4 T. The transition temperature was given to be 89.8 K for the midpoint of the resistive transition with ΔT c=3.7 K. The slope of the critical field was -1.6 T/K. The upper critical field H c2(0) was estimated to be 96 T according to the Werthamer, Helfand and Hohenberg expression for dirty limit. It is expected that the resistivity does not appear up to 61 T at 0 K in the framework of the BCS-WHH theory.