Evidence of zero point fluctuation of vortices in a very weakly pinned a-MoGe thin film

TL;DR

This study presents evidence of quantum zero-point vortex fluctuations in a weakly pinned a-MoGe thin film, observed via scanning tunneling spectroscopy, revealing persistent soft gaps at vortex cores due to vortex motion.

Contribution

It provides experimental evidence of vortex zero-point fluctuations in a superconductor, linking vortex dynamics to quantum effects in a weakly pinned thin film.

Findings

Persistent soft gap at vortex core center.

Vortex fluctuation amplitude varies with magnetic field.

Quantum zero-point motion of vortices is consistent with data.

Abstract

In a Type II superconductor, the vortex core behaves like a normal metal. Consequently, the single-particle density of states in the vortex core of a conventional Type II superconductor remains either flat or (for very clean single crystals) exhibits a peak at zero bias due to the formation of Caroli-de Gennes-Matricon bound state inside the core. Here we report an unusual observation from scanning tunneling spectroscopy measurements in a weakly pinned thin film of the conventional s-wave superconductor a-MoGe, namely, that a soft gap in the local density of states continues to exist even at the center of the vortex core. We ascribe this observation to rapid fluctuation of vortices about their mean position that blurs the boundary between the gapless normal core and the gapped superconducting region outside. Analyzing the data as a function of magnetic field we show that the variation of fluctuation amplitude as a function of magnetic field is consistent with quantum zero-point motion of vortices.