Dependence of vortex liquid phase of Pb-In alloy on indium concentration

Abstract Isothermal current–voltage ( J – E ) characteristics have been measured for films of lead (Pb)–indium (In) alloys, Pb 100− x In x ( x =8.23, 4.0 and 2.0 wt.%) in the mixed state. The isothermal log J vs. log E curves similar to those characterizing the vortex glass–vortex liquid (VL) transition in copper oxide superconductors have been observed, though the reversibility of magnetization curve for bulk samples in the mixed state could not be detected within the experimental accuracy in the present study. Using Fisher’s theoretical relations, the transition temperature T g ( H ), the static and dynamical critical exponents are determined. The variation of the exponents with H in low magnetic fields reported in high temperature superconductors was not observed. The upper critical magnetic field H c2 ( T ) determined by resistivity vs. temperature in the mixed state increases with increasing In concentration, but the T g ( H ) is almost independent of the In concentration. A region between H c2 ( T ) and T g ( H ) in a plane of H and T , which may be considered as the VL region, becomes wider with increasing In concentration.