Strong-pinning regimes by spherical inclusions in anisotropic type-II superconductors*

To make superconductors technologically relevant, it is crucial to immobilize flux lines (vortices) threading the material. Capturing the pinning mechanism starting from microscopic interactions of vortices with defects poses a very difficult problem. The theory of strong vortex pinning provides a starting point to address this problem. We revisit the different regimes of strong-pinning theory and investigate them using large-scale numerical solutions of the time-dependent Ginzburg-Landau equations [1]. We explore the magnetic-field dependences of the critical current, j_c(B), for superconductors containing spherical inclusions with different sizes and densities. Within a wide range of parameters, the vortex configuration is disordered and features a power-law decay of j_c(B) ∝ B^-α, where the power index α decreases with the particle density. We find a first-order transition of the pinning ground state towards double-occupancy of defects leading to a non-monotonic pin-breaking force and peak effect. Our results provide a framework for interpretation of pinning properties of real materials and call for further generalization of theory. [1] R. Willa et al., Superc. Sci. Tech. 2017, arXiv:1708.01653