Mechanism of vortex motion in high-temperature superconductors

Different models for the description of vortex motion in real type-II superconducting systems are introduced and applied to high- and low-T-c superconductors, ranging from pin breaking in homogeneous systems to different vortex shear models, which describe the plastic flow of vortices within percolation paths across the superconductor taking into account a distribution of superconducting properties. It is demonstrated, that collective pinning (for instance caused by oxygen vacancies) is sufficiently strong to provide the necessary intrinsic volume pinning force in high-T-c material ifa single vortex approach is applied. Thus, inhomogeneities in the sample have to be considered, which lead to a flux shear dominated mechanism of vortex motion in real systems. This mechanism automatically explains a number of interesting phenomena and properties of high-T-c material: the Arrhenius-like phase transition, the 's'-shape of the voltage-current characteristics in the double logarithmic plot, the existence of a reversible regime close to B-c2, and the correct temperature scaling, field scaling and magnitude of the volume pinning force. Finally, the inhomogeneity of the superconducting material is derived from experimental data via inversion schemes obtained for different models. The resulting distribution functions for local superconducting properties are comparable for all schemes. Possible explanations for the shape of the distributions are given.