Superconducting Upper Critical Field Hc2 of High-Tc Y-Ba-Cu-O Compound System

Publisher Website
Google Scholar
Abstract
Superconducting transition in the magnetic field up to 9 T and upper critical field H c2 near T c were investigated for several samples which have the nominal composition Y1-y Ba y CuO x with (a) y=0.60 or (b) y=0.65 and x undetermined. (a)- and (b)-samples show zero-resistance around 88 K and multi-phase and almost-single-phase behaviors, respectively, in the magnetic field, being consistent with a recently proposed model of YBa2Cu3O x for a 90 K-range phase. In a (b)-sample, a very large value of (-dH c2/dT) of 3.0∼3.5 T/K or 4.0∼4.5 T/K was observed, depending on if H c2 was taken at the 50% of the normal state resistance R n or the 90%. Based on a theory assuming no paramagnetic limiting, this means H c2(0) of 200 or 250 T, the highest one among the reported values.