Year: 2026
Type: preprint
Abstract: In flat band superconductors, quantum geometry, rather than kinetic energy, governs pairing and transport. However, how this geometry manifests in the response to a local, individually addressable impurity remains largely unexplored. Here, we study the Yu-Shiba-Rusinov (YSR) bound state induced by a magnetic adatom that hybridizes with every orbital of a two-dimensional flat band superconductor, and characterize its spatial profile using two quantities: the quadratic spread $Q_S$ and the localization length $ξ$. We show that $Q_S$ is not set by the quantum metric alone, as geometric corrections arising from inter-orbital interference and, more importantly, from the anisotropy of the adatom-lattice hybridization contribute on equal footing, making $Q_S$ strongly impurity dependent and tunable. On the other hand, $ξ$ emerges from the projection onto the flat band alone and is a universal property set by the overlap of compact localized states. All impurity dependence is instead isolated in the prefactor of the wavefunction whose magnitude correlates directly with $Q_S$. We, therefore, report a clean separation between universal and impurity-tunable physics from the induced YSR bound state in these systems, and confirm our results numerically via exact diagonalization.
Source: arXiv (Cornell University)
Authors: Cardoso, Simão S., Mesaros, A., Simon, P.
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7206189559