High Field Properties of Superconducting Y_xBa_1-xCu-Oxides

Abstract

The transition temperature, T c , the upper critical field, H c2 ( T ), and the critical current density, J c ( H ), at 4.2 K have been studied in high- T c Y x Ba 1- x Cu-Oxide system. Two maxima in T c around x =0.33 and 0.4 have been observed. The slope d H c2 mid /d T near T c for the sample x =0.4 is -1.5 T/K, resulting in H c2 at 0 K higher than 85 T by an extrapolation according to the WHH theory. Although the J c value of ∼3.5 A/cm 2 at 15 T is very low, it decreases only 10% even at 27 T, showing high potential for practical use at high fields when J c is raised by the introduction of strong pinning centers in this material.