Muon-Spin Rotation Measurements of the Magnetic Field Dependence of the Vortex-Core Radius and Magnetic Penetration Depth in NbSe2

TL;DR

This study uses muon-spin rotation to investigate how the vortex-core radius and magnetic penetration depth in NbSe2 change with magnetic field, revealing behaviors that challenge existing theories and introducing new phenomenological modeling.

Contribution

It provides the first measurement of the linear increase of in-plane magnetic penetration depth with magnetic field in a conventional superconductor and challenges the dirty-limit microscopic theory.

Findings

Vortex-core radius decreases sharply with increasing magnetic field.

In-plane magnetic penetration depth increases linearly with magnetic field.

Results do not align with existing dirty-limit microscopic theory.

Abstract

Muon-spin rotation spectroscopy has been used to measure the internal magnetic field distribution in NbSe2 for Hc1 << H < 0.25 Hc2. The deduced profiles of the supercurrent density indicate that the vortex-core radius in the bulk decreases sharply with increasing magnetic field. This effect, which is attributed to increased vortex-vortex interactions, does not agree with the dirty-limit microscopic theory. A simple phenomenological equation in which the core radius depends on the intervortex spacing is used to model this behaviour. In addition, we find for the first time that the in-plane magnetic penetration depth increases linearly with H in the vortex state of a conventional superconductor.