Nonlinear I similar to V characteristic and magnetic relaxation in high-T-c superconductors

Large-scale applications of high-temperature superconductors require large critical current density J(c). The limit of utilization is determined by th e practical resistivity criterion and the current-voltage characteristic of a superconductor which is highly nonlinear in these materials, Various mod els 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 c onsistent description of different regimes of flux motion, We compare this equation with recent pertinent experiments and find fair agreements.