Coherent coupling between vortex bound states and magnetic impurities in 2D layered superconductors

TL;DR

This study reveals that magnetic impurities induce a long-range electron-hole asymmetry in vortex bound states of 2D layered superconductors, observable both theoretically and experimentally, with implications for understanding coupled superconducting states.

Contribution

The paper demonstrates, both theoretically and experimentally, that magnetic impurities cause a long-range electron-hole asymmetry in vortex bound states in 2D superconductors, influenced by band character.

Findings

Magnetic impurities induce a long-range electron-hole asymmetry in vortex states.

The asymmetry depends on the band character of the superconductor.

Experimental and theoretical results are consistent and show emergent axial asymmetry.

Abstract

Bound states in superconductors are expected to exhibit a spatially resolved electron-hole asymmetry which is the hallmark of their quantum nature. This asymmetry manifests as oscillations at the Fermi wavelength, which is usually tiny and thus washed out by thermal broadening or by scattering at defects. Here we demonstrate theoretically and confirm experimentally that, when coupled to magnetic impurities, bound states in a vortex core exhibit an emergent axial electron-hole asymmetry on a much longer scale, set by the coherence length. We study vortices in 2H-NbSe$_2$ and in 2H-NbSe$_{1.8}$S_{0.2}$ with magnetic impurities, characterizing these with detailed Hubbard-corrected density functional calculations. We find that the induced electron-hole imbalance depends on the band character of the superconducting material. Our results open interesting prospects for the study of coupled superconducting bound states.