Phase transition like electrical behaviour in YBa2Cu3O7:Y2BaCuO5composites

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Abstract
Nano-volt measurement techniques have been used to study the electrical characteristics of superconducting YBa2Cu3O7:Y2BaCuO5 composites. The families of current-voltage (I-V) curves obtained by making measurements at a number of temperatures display the characteristic features of a phase transition, where the “transition temperature”, Tp , is a strong function of the composition and of the magnetic field. The data is compared with the scaling behaviour expected of Kosterlitz-Thouless pairing-depairing transitions and vortex-glass phase transitions and with recent flux flow resistivity models for inhomogeneous systems. In low magnetic fields we find the same family of I-V curves at each magnetic field. Any particular I-V curve may be obtained for a locus of points in the temperature-magnetic field plane. We note that this places severe restrictions on the form of theoretical predictions.