# A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities

## TL;DR

This study combines PCT and LE-muSR techniques to analyze surface superconducting properties of niobium films prepared by various sputtering methods, correlating findings with RF cavity performance and revealing surface paramagnetism.

## Contribution

It provides a comparative analysis of surface superconducting properties of niobium films prepared by different sputtering techniques using combined PCT and LE-muSR methods.

## Key findings

- Degraded surface properties lead to lower RF quality factors.
- Surface paramagnetism is observed on all samples, especially HIPIMS-prepared films.
- Surface superconducting properties correlate with RF performance.

## Abstract

Point contact tunneling (PCT) and low energy muon spin rotation (LE-muSR) are used to probe, on the same samples, the surface superconducting properties of micrometer thick niobium films deposited onto copper substrates using different sputtereing techniques: diode, dc magnetron (dcMS) and HIPIMS. The combined results are compared to radio-frequency tests performances of RF cavities made with the same processes. Degraded surface superconducting properties are found to yield lower quality factors and stronger Q slope. In addition, both techniques find evidence for surface paramagnetism on all samples and particularly on Nb films prepared by HIPIMS.