# Nodeless superconductivity and the peak effect in the quasi-skutterudites $\mathrm{Lu}_3\mathrm{Os}_4\mathrm{Ge}_{13}$ and $\mathrm{Y}_3\mathrm{Ru}_4\mathrm{Ge}_{13}$

## TL;DR

This study reveals nodeless, multi-gap superconductivity and the peak effect in flux line arrangements in Lu3Os4Ge13 and Y3Ru4Ge13, using resistivity, susceptibility, and penetration depth measurements.

## Contribution

It provides new evidence of nodeless, multi-gap superconductivity and the peak effect in these quasi-skutterudite materials, expanding understanding of their superconducting properties.

## Key findings

- Nodeless superconductivity confirmed in both materials.
- Presence of multiple superconducting gaps suggested.
- Observation of the peak effect indicating flux line rearrangement.

## Abstract

We report an investigation of the superconducting states of $\mathrm{Lu}_3\mathrm{Os}_4\mathrm{Ge}_{13}$ and $\mathrm{Y}_3\mathrm{Ru}_4\mathrm{Ge}_{13}$ single crystals by measurements of the electrical resistivity, ac susceptibility and London penetration depth. The analysis of the penetration depth and the derived superfluid density indicates the presence of nodeless superconductivity and suggest that there are multiple superconducting gaps in both materials. Furthermore, ac susceptibility measurements of both compounds display the peak effect in the low temperature region of the $H-T$ phase diagram. This anomalous increase of the critical current with field gives an indication of a change of the arrangement of flux lines in the mixed state, as found in some of the isostructural stannide materials.