Comparison of the scaling analysis of the mixed-state magnetization data with direct measurements of the upper critical field in Y-123

Abstract

By comparison of recent direct measurements of the temperature dependence of the upper critical field Hc2 in an YBa2Cu3O7−x high-Tc superconductor with the scaling analysis of magnetization data, collected in fields H ≪ Hc2, we demonstrate that that the temperature dependence of the Ginzburg-Landau parameter κ is negligible. Another conclusion is that the normalized temperature dependence of Hc2 is independent of the orientation of the magnetic field in respect to crystallographic axes of the sample. We also discuss that isotropy of the temperature dependence of Hc2 straightforwardly follows from the Ginzburg-Landau theory if κ does not depend on temperature.