Between types I and II: Intertype flux exotic states in thin superconductors

Abstract

The Bogomolnyi point separates superconductivity types I and II while itself hiding infinitely degenerate magnetic flux configurations, including very exotic states (referred to here as flux “monsters”). When the degeneracy is removed, the Bogomolnyi point unfolds into a finite, intertype domain in the phase diagram between types I and II. One can expect that in this case the flux monsters can escape their “prison” at the Bogomolnyi point, occupying the intertype domain and shaping its internal structure. Our calculations reveal that such exotic flux distributions are indeed stable in the intertype regime of thin superconductors made of a type-I material, where the Bogomolnyi degeneracy is removed by stray magnetic fields. They can be classified into three typical patterns that are qualitatively different from those in types I and II: superconducting islands separated by vortex chains; stripes/worms/labyrinths patterns; and mixtures of giant vortices and vortex clusters. Our findings shed light on the problem of the interchange between types I and II, raising important questions on the completeness of the textbook classification of the superconductivity types.

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