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

Isothermal current-voltage (J-E) characteristics have been measured for films of lead (Pb)-indium (In) alloys, Pb_100-xIn_x (x=8.23, 4.0 and 2.0 wt.%) in the mixed state. The isothermal logJ vs. logE 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.