Instability driven formation of domains in the intermediate state of type-I superconductors

TL;DR

This study investigates the formation of normal-state domains in type-I superconductors, revealing that domain shapes are driven by instability thresholds and flux penetration rather than mutual domain interactions.

Contribution

It demonstrates that domain shape transitions are governed by instability thresholds and flux penetration effects, challenging the assumption of mutual interactions in self-organized patterns.

Findings

Threshold surface area for shape transition matches theoretical predictions.

Domain shapes are influenced by elongation instability and flux bursts.

Mutual domain interactions are not the primary factor in pattern formation.

Abstract

The formation of normal-state domains in type-I superconducting indium films is investigated using the high resolution magneto-optical imaging technique. The observed patterns consist of coexisting circular and lamellar normal-phase domains surrounded by the superconducting phase. The distribution of domain surface areas is found to exhibit a threshold, above which only the lamellar shape is observed. We show that this threshold coincides with the predicted critical surface area for the elongation instability of the circular shape. The partition of the normal phase into circular and lamellar domains is determined by the combined effects of the elongation instability and the penetration of magnetic flux by bursts at the early stage of pattern formation. It is not governed by mutual interactions between domains, as usually assumed for self-organized systems.