Necklace-like pattern of vortex bound states

TL;DR

This paper reports a novel necklace-like vortex pattern in an iron-based superconductor, arising from interference effects due to disorder and symmetry breaking, offering new insights into vortex physics.

Contribution

It introduces a new vortex pattern in superconductors caused by off-shell interference, expanding understanding beyond traditional circular vortex states.

Findings

Discovery of necklace-like vortex pattern in KCa2Fe4As4F2

Theoretical explanation involving interference of vortex bound states

Observation enabled by small Fermi energy and wave vector conditions

Abstract

Vortex is a topological defect in the superconducting condensate when a magnetic field is applied to a type-II superconductor, as elucidated by the Ginzburg-Landau theory. Due to the confinement of the quasiparticles by a vortex, it exhibits a circular shaped pattern of bound states with discrete energy levels, as predicted by the Caroli-de Gennes-Matricon theory in 1964. Here, however, we report a completely new type of vortex pattern which is necklace-like in an iron-based superconductor KCa2Fe4As4F2. Our theoretical analysis shows that this necklace-like vortex pattern arises from selective off-shell interference between vortex bound states of opposite angular momenta in the presence of rotational symmetry breaking due to disorders. This fascinating effect can be observed in a system with a small Fermi energy and wave vector, conditions fortuitously met in our samples. Our results not only disclose a novel vortex structure but also provide insights into comprehending the physics of the superconducting condensate.