Glass behavior and the H-T phase diagram of the high-Tc ceramic superconductors YBa2Cu3O7, EuBa2Cu3O7, and GdBa2Cu3O7.

Abstract

We report systematic field-cooled (FC) and zero-field-cooled (ZFC) diamagnetic susceptibility measurements in polycrystalline samples of the high-${T}_{c}$ oxide superconductors R${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$, where R=Y, Eu, or Gd. We focus mainly on the temperature range near ${T}_{c}$, where the FC and ZFC curves split up below a characteristic temperature, similar to the behavior of spin glasses. This temperature depends on the applied magnetic field and defines a crossover line in the H-T plane separating ergodic and nonergodic behavior, in close resemblance to what is found in conventional spin glasses. We suggest that this is a general characteristic of the ceramic oxide superconductors. Moreover, our data allow us to obtain a more detailed high-temperature H-T phase diagram, where a lower temperature bound for the superconducting glasslike state is proposed.