Glass behavior and the h-t phase diagram of the high-tc ceramic superconductors yba2cu3o7, euba2cu3o7 and gdba2cu3o7

Abstract

We report systematic field-cooled (PC) and zero-field-cooled (ZPC) diamagnetic susceptibility measurements in polycrystalline samples of the high-Tc oxide superconductors RBa2Cu30 7, where R =Y, Eu, or Gd. We focus mainly on the temperature range near T0 where the PC and ZPC 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-Tplane 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-Tphase diagram, where a lower temperature bound for the superconducting glasslike state is proposed.