Flux-line cutting in type II superconductors

Abstract

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 a (~ O)is thenshown 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 GinzburgLandau theory. Here two competing interactions determine the behavior. Electromagnetic repulsion (0 < a < 7r/2) varies as cos a and decays over distances scaled by the penetration depth A, while core attraction is independent of a and varies over distances scaled by the coherence length ~.The force is always repulsive at large flux-line separation (19 < ~ < Ir/2) and its maximum decreases rapidly as K decreases, so that flux-line cutting is expected to be more probable in low-K materials. The calculations provide a basis for explaining longitudinal flux-flow resistance as well as some intriguing magnetization behavior in the same configuration.

Flux cutting in high-Tcsuperconductors

“…Since then, the force free configurations and transverse vortex motion in longitudinal currents were addressed in many theoretical works but still remain a hypothetical concept. Two crossing vortices should experience a long-range repulsion due to the λ-shell of supercurrents, while the intersection of the normal cores will provide their short-range attraction [53]. This could yield pinning of vortices by transverse vortices.…”

“…This could yield pinning of vortices by transverse vortices. The resulting pinning potential was first assumed to be very high (~normal core condensation energy), but subsequent calculations showed only moderate values of the cutting barrier U x [53]. Account of the mutual bending of vortices near the intersection point revealed additional attraction and further reduction of U x [54][55][56][57].…”

Measurements on magnetized GdBCO pellets subjected to small transverse ac magnetic fields at very low frequency: Evidence for a slowdown of the magnetization decay

“…The situation is more intricate when the field is applied transversally to the remnant magnetization . This effect, called either "abnormal transverse magnetic field effect", "collapse of the static magnetization" or "crossed-field demagnetisation" was observed on low-Tc wires [21,28,43], bulk (RE)BCO materials [22,25,28,33,34,40], MgB2 [44] and recently on stacks of 2G tapes [45]. Up to now, however, the exact processes of the magnetization decay in the case of a crossed field configuration are not completely identified.…”

Theory of Flux Cutting for Type-II Superconducting Plates at Critical State

“…Given that cutting is energetically plausible, they found that flux-line cutting is an effective disentanglement mechanism of flux lines; and that the cutting energy barrier, in the case of twisted flux lines, is lower for the rigid two-flux-lines case [11,12]. Several groups, for example, M.A.R.…”