Evidence for a low-gap component in compressively stressed niobium thin films

@misc{paustian2026evidence,
  title = {{Evidence for a low-gap component in compressively stressed niobium thin films}},
  author = {J. T. Paustian and Maciej Olszewski and Kiichi Okubo and Lingda Kong and B. L. T. Plourde and Ethan G. Arnault and Caleb W. Fink and Valla Fatemi and Ivan V. Pechenezhskiy},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.26714},
  eprint = {2609.26714},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.26714},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Evidence for a low-gap component in compressively stressed niobium thin films
AU  - J. T. Paustian
AU  - Maciej Olszewski
AU  - Kiichi Okubo
AU  - Lingda Kong
AU  - B. L. T. Plourde
AU  - Ethan G. Arnault
AU  - Caleb W. Fink
AU  - Valla Fatemi
AU  - Ivan V. Pechenezhskiy
PY  - 2026
DA  - 2026/09/22
PB  - arXiv
DO  - 10.48550/arxiv.2609.26714
UR  - https://arxiv.org/abs/2609.26714
AB  - We investigate the microwave response of sputtered Nb films as a function of biaxial film stress. Although transport measurements show nearly identical superconducting transition temperatures (9.0± 0.2K) and residual resistance ratios across the stress series, microwave resonators fabricated from highly compressive films exhibit enhanced temperature-dependent loss and larger frequency shifts. A conventional single-phase Mattis--Bardeen description yields an effective critical temperature of 2.4±0.2K, approximately a factor of four below the value obtained from transport measurements. We show that the data are instead consistent with the presence of an additional low-gap component whose contribution increases with compressive stress. These results show that conventional transport measurements can overlook stress-dependent low-energy excitations that strongly influence microwave performance.
ER  -