Flux-line cutting in type II superconductors

Experimental evidence for flux-line cutting in superconductors (intersection and cross-joining of singly quantized vortices) is briefly reviewed. The interaction energy between two straight vortices tilted at an angle α (not =0) is then shown to be finite in the London model, i.e., in the limit of vanishing core radius. Next, the activation energy and maximum interaction force are calculated for the vortices in an analytic approximation to the Ginzburg--Landau theory. Here two competing interactions determine the behavior. Electromagnetic repulsion (0<α<π/2) varies as cos α and decays over distances scaled by the penetration depth lambda, while core attraction is independent of α and varies over distances scaled by the coherence lenght xi. The force is always repulsive at large flux-line separation (0<α<π/2) and its maximum decreases rapidly as kappa decreases, so that flux-line cutting is expected to be more probable in low-kappa materials. The calculations provide a basis for explaining longitudinal flux-flow resistance as well as some intriguing magnetization behavior in the same configuration