# On the interpretation of muon-spin-rotation experiments in the mixed state of type-II superconductors

## TL;DR

This paper critiques previous interpretations of muon-spin-rotation experiments in type-II superconductors, emphasizing the importance of accurate theoretical models and demonstrating the utility of Brandt's numerical calculations for data analysis and distinguishing superconductor types.

## Contribution

It highlights the limitations of earlier models, reanalyzes experimental data using Brandt's calculations, and advocates for their broader application in superconductor research.

## Key findings

- Previous claims about lambda's magnetic field dependence are based on inaccurate models.
- Brandt's numerical calculations provide reliable analysis tools for experimental data.
- The approach can differentiate between conventional and unconventional superconductors.

## Abstract

We argue that claims about magnetic field dependence of the magnetic field penetration depth lambda, which were made on the basis of moun-spin-rotation studies of some superconductors, originate from insufficient accuracy of theoretical models employed for the data analysis. We also reanalyze some of already published experimental data and demonstrate that numerical calculations of Brandt [E.H. Brandt, Phys. Rev. B 68, 54506 (2003)] may serve as a reliable and powerful tool for the analysis of the data collected in experiments with conventional superconductors. Furthermore, one can use this approach in order to distinguish between conventional and unconventional superconductors. It is unfortunate that these calculations have practically never been employed for such analyses.