The nature of the relaxation of resistivity in high-T-c superconductors

The relaxation of resistivity R-ff(t) in high-T-c superconductors is discussed both experimentally and theoretically. The two-kind-of-flux-creep model is proposed. The flux related to the irreversible magnetization part is defined as relaxation flux, which may creep under the Lorentz force of an average transport current density J(t) and cause a time-dependent resistivity. The creep of conventional flux under the Lorentz force of J(t) causes a time-independent resistivity. A general formula of R-ff(t) is obtained. A specific R-ff(t) formula is derived from the general one, using the logarithmic U-J relation, which describes quantitatively the experimental data well, Experiments support the proposed model. (C) 1997 Elsevier Science B.V.