MAGNETIC-FIELD-DEPENDENT VORTEX-GLASS SCALING BEHAVIOR IN V-DOPED YBA2CU3O7-Y SYSTEM

The scaling behaviour of vortex-glass superconductivity is studied, by measuring the resistive transition as well as the I-V curve under a v ariety of magnetic fields, in a series of V doped YBa2Cu3O7-y samples with different grain sizes. The equilibrium phase boundary line betwee n the normal and superconducting phases in the H-T plane obtained by f itting the resistive transition is consistent with that obtained by th e I-V curve measurements. As the magnetic field is lower than a certai n value, H-s, the scaling exponents are magnetic-field independent, bu t at H=H-s, they begin to increase with the magnetic field and gradual ly get saturation. The switch field, H-s, decreases with decreasing th e grain size in the samples. The results show that the magnetic-field- dependent scaling behaviour of the I-V curve observed in weak-link con taining systems originates from the transition of a ''weak'' vortex-gl ass state to a ''strong'' vortex-glass state.