The scaling of the current voltage characteristics of the YBa₂Cu₃O₇:Y₂BaCuO₅ composites

Abstract

We have investigated features in the current voltage (I—V) characteristics of YBa₂Cu₃O₇:Y₂BaCuO₅ composite sinters which indicate the occurrence of a second-order phase transition. For each sinter composition similar families of characteristics are found for a wide range of magnetic fields. The relation between V and I is seen to be of the form V = f(I, ζ(B, T)) where a single parameter ξ contains all of the field and temperature dependence. The locus of points in the B, T plane for which ζ(B, T) is a constant have been examined, and a low field and a high field régime have been identified. Samples of different composition show families of I—V characteristics which scale onto one another in a simple way, hence we are led to suppose the V = f(I, ζ(B, T, p)) where p is the dilution fraction. Data taken at temperatures below the phase transition agrees well with a simple scaling picture of dissipation close to a second order phase transition, with exponents which are independent of magnetic field and composition. Above the transition, however, the behaviour is more complex.

Key Words:

• High temperature superconductors
• sinters
• phase transition
• scaling
• vortex-glass