Computer Simulation of Flux Pinning in Type-II Superconductors

Random point pinning of ideal or defective flux-line lattices is simulated on a computer. For weak pins, Larkin and Ovchinnikov's two-dimensional collective pinning is confirmed: $j_c=\mathrm{const}\times \frac{n_p〈{f_p}^2〉}{R_p{c}_{66}}$ ($j_c$ is the critical current; $n_p$, $f_p$, and $R_p$ are the density, force, and range of pins; and $c_{66}$ is the shear modulus). The constant is determined. Defective lattices are pinned more strongly by factors 1.3 to 3, explaining the observed history effect. A pronounced jump in the curves $j_c\left(f_p\right)$ indicates the onset of plastic deformation.