Quantum limiting behaviors of a vortex core in an anisotropic gap superconductor

TL;DR

This study investigates the quantum behavior of vortex cores in an anisotropic superconductor using high-resolution scanning tunneling spectroscopy, revealing detailed spectral features and their theoretical understanding.

Contribution

It provides the first detailed experimental observation and theoretical analysis of vortex core states in an anisotropic gap superconductor at atomic resolution.

Findings

Discretized bound states at the vortex core are observed.

A second subpeak related to the fourfold gap symmetry is identified.

Particle-hole asymmetry and quantum oscillations are detected.

Abstract

Quantized bound states at a vortex core are discretized in YNi$_2$B$_2$C. By using scanning tunneling spectroscopy with an unprecedented 0.1 nm spatial resolution, we find and identify the localized spectral structure, where in addition to the first main peak with a positive low energy, a second subpeak coming from the fourfold symmetric gap structure is seen inside the energy gap. Those spectral features are understood by solving the Bogoliubov-de Gennes equation for a fully three-dimensional gap structure. A particle-hole asymmetric spectrum at the core site and quantum oscillation in the spectra are clearly observed.