# Scanning Tunneling Spectroscopy in the Superconducting State and Vortex Cores of the beta-pyrochlore KOs2O6

## TL;DR

This study uses scanning tunneling spectroscopy to investigate the superconducting gap, vortex lattice, and vortex core properties of KOs2O6, revealing fully-gapped superconductivity, vortex lattice structure, and field-dependent vortex core size.

## Contribution

First scanning tunneling spectroscopy measurements on KOs2O6 revealing detailed vortex core structure and superconducting gap anisotropy.

## Key findings

- Fully-gapped superconductivity with 30% gap anisotropy
- Hexagonal Abrikosov vortex lattice observed
- Vortex core size decreases with increasing magnetic field

## Abstract

We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc = 9.6 K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully-gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31-40 {\AA}, in agreement with the value derived from the upper critical field Hc2. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.