Active control of thermomagnetic avalanches in superconducting Nb films with tunable anisotropy

Abstract

Active triggering and manipulation of ultrafast flux dynamics in superconductors are demonstrated in films of Nb. Controlled amounts of magnetic flux were injected from a point along the edge of a square sample, which at 2.5 K responds by nucleation of a thermomagnetic avalanche. Magneto-optical imaging was used to show that when such films are cooled in the presence of in-plane magnetic fields they become anisotropic, and the morphology of the avalanches change systematically, both with the direction and magnitude of the field. The images reveal that the avalanching dendrites consistently bend towards the direction perpendicular to that of the in-plane field. The effect increases with the field magnitude, and at 1.5 kOe the triggered avalanche becomes quenched at the nucleation stage. The experimental results are explained based on a theoretical model for thermomagnetic avalanche nucleation in superconducting films, and by assuming that the frozenin flux generates in-plane anisotropy in the film thermal conductance. The results demonstrate that applying in-plane magnetic fields to film superconductors can be a versatile external tool for controlling their ultrafast flux dynamics.

Nucleation and propagation of thermomagnetic avalanches in thin-film superconductors (Review Article)

“…¼ 20 Oe. Quantitative measure ments 89 of the anisotropy in the critical sheet currents, J T c and J L c , see Fig. 16, right panel, found that their ratio is well described by the qubic dependence, 88…”

“…Separate measurements were required to decide whether the anisotropy is due to reduced pinning of the perpendicular vortices when moving parallel the frozen-in in-plane vortices, or enhanced pinning of perpendicular vortices traversing the array of the in-plane ones, or both. To resolve this question a local flux injector, 89 was used, where the square Nb sample was extended by two strips forming an inverted Vshape allowing for a transport current to be passed through a small region of the square near its lower edge, see Fig. 17.…”

Selective triggering of magnetic flux avalanches by an edge indentation

“…It would be interesting to extend and confront the present investigation to the case of current induced flux avalanches caused by flux focussing effect as experimentally addressed in Ref. [36,37]…”

Propriedades magnéticas e supercondutoras de redes de nanofios de Ni acopladas a filmes de Nb

“…A Fig.6.11 mostra a dependência genérica do campo magnético perpendicular limiar em função da corrente crítica para filmes supercondutores, onde pode-se observar que o fato de termos um incremento no campo limiar para o começo de avalanches de vórtices implica na diminuição da densidade de corrente crítica no supercondutor. Dessa forma, podemos afirmar que a presença de nanofios magnéticos na matriz porosa estaria contribuindo para a diminuição da corrente Figura 6.11: Curva genérica do campo perpendicular limiar para o inicio de avalanches termomagnéticas num filme supercondutor em função da densidade de corrente crítica [137,138]. crítica no filme supercondutor.…”

“…. 110 6.11 Curva genérica do campo perpendicular limiar para o inicio de avalanches termomagnéticas num filme supercondutor em função da densidade de corrente crítica [137,138]…”