Nonlinear I/spl sim/V characteristic and magnetic relaxation in high-T/sub c/ superconductors

Large-scale applications of high-temperature superconductors require large critical current density J/sub c/. The limit of utilization is determined by the practical resistivity criterion and the current voltage characteristic of a superconductor which is highly nonlinear in these materials. Various models with different barrier-current dependencies U(J) have been developed to describe the flux motion in them but questions still remain. We show that these models may be unified to a general materials equation which gives a consistent description of different regimes of flux motion. We compare this equation with recent pertinent experiments and find fair agreements.