Concerning factors which determine whether flux-lattice shear or pin breaking limits the critical current density of superconductors

An elementary model that illustrates the conditions under which flux-lattice shear, rather than pin breaking, limits the critical current density is presented. An expression for the shear strength of the flux-lattice, based on the plasticity of metals and alloys, is used to derive the critical current density, including the effect of thermal activation in the flux creep regime. Expressions are also derived for the flow stress and dislocation density of the flux-line lattice (FLL) and are combined to yield the magnetic-field- and temperature-dependent critical current density in the absence of thermal activated flux creep. The rate theory of plastic deformation is used to derive the electric-field vs. current-density relation and J/sub c/ to be expected when thermally activated processes make the dominant contribution to FLL shear.<>