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

TL;DR

This study demonstrates how in-plane magnetic fields can actively control the shape and behavior of thermomagnetic avalanches in superconducting Nb films, enabling tunable flux dynamics through anisotropy.

Contribution

It introduces a method to manipulate ultrafast flux avalanches in superconductors using external magnetic fields to induce anisotropy.

Findings

Avalanche morphology changes systematically with in-plane field direction and magnitude.

Avalanches bend perpendicular to the in-plane magnetic field direction.

High in-plane fields can suppress avalanches at nucleation.

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 frozen-in 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.