Long range coherent magnetic bound states in superconductors

TL;DR

This paper reports the discovery of long-range coherent magnetic bound states around a magnetic impurity in a superconductor, revealing potential for new quantum interactions and topological phases.

Contribution

It demonstrates the existence of a novel long-range magnetic quantum state extending up to 12 nm, linked to the superconductor's coherence length, and provides a theoretical explanation for these phenomena.

Findings

Observation of a star-shaped pattern extending 12 nm from impurity

Detection of short-scale interference fringes with particle-hole asymmetry

Theoretical model linking features to electronic band structure

Abstract

The quantum coherent coupling of completely different degrees of freedom is a challenging path towards creating new functionalities for quantum electronics. Usually the antagonistic coupling between spins of magnetic impurities and superconductivity leads to the destruction of the superconducting order. Here we show that a localized classical spin of an iron atom immersed in a superconducting condensate can give rise to new kind of long range coherent magnetic quantum state. In addition to the well-known Shiba bound state present on top of an impurity we reveal the existence of a star shaped pattern which extends as far as 12 nm from the impurity location. This large spatial dispersion turns out to be related, in a non-trivial way, to the superconducting coherence length. Inside star branches we observed short scale interference fringes with a particle-hole asymmetry. Our theoretical approach captures these features and relates them to the electronic band structure and the Fermi wave length of the superconductor. The discovery of a directional long range effect implies that distant magnetic atoms could coherently interact leading to new topological superconducting phases with fascinating properties.