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

Abstract: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 ($9.0\pm 0.2$K) 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 $2.4\pm0.2$K, 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.

Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)

arXiv:2609.26714 [quant-ph]

(or arXiv:2609.26714v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2609.26714 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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