THE SCALING OF THE CURRENT-VOLTAGE CHARACTERISTICS OF THE YBA2CU3O7-Y2BACUO5 COMPOSITES

We have investigated features in the current voltage (I-V) characteris tics of YBa2Cu3O7:Y2BaCuO5 composite sinters which indicate the occurr ence of a second-order phase transition. For each sinter composition s imilar families of characteristics are found for a wide range of magne tic fields. The relation between V and I is seen to be of the form V = f(I, xi(B, T)) where a single parameter xi contains all of the field and temperature dependence. The locus of points in the B, T plane for which xi(B, T) is a constant have been examined, and a low field and a high field regime have been identified. Samples of different composit ion 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, xi(B, T, p)) where p is the dilution fraction. Data taken at temperatures below th e phase transition agrees well with a simple scaling picture of dissip ation close to a second order phase transition, with exponents which a re independent of magnetic field and composition. Above the transition , however, the behaviour is more complex.