Microwave Response of Superconductors with Paramagnetic Impurities
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arXiv
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| Hauptverfasser: | , |
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| Format: | Preprint |
| Veröffentlicht: |
2025
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| author | Zarea, Mehdi Sauls, J. A. |
| author_facet | Zarea, Mehdi Sauls, J. A. |
| contents | We develop theoretical methods to predict the effects of paramagnetic impurities on the microwave response of conventional spin-singlet superconductors. Our focus is on superconducting devices and resonators with low concentrations of impurities and exchange interactions with conduction electrons. We connect the sub-gap quasiparticle spectrum generated by pair-breaking to the frequency and temperature dependence of the conductivity for superconductors operating at microwave frequencies. We report theoretical results for superconducting device performance -- dissipation, quality factor and frequency shift anomalies -- based on self-consistent calculations of the current response and penetraion of the electromagnetic field at the vacuum-superconducting interface. Key results include the prediction of a non-monotonic anomaly in the low-frequency superfluid fraction and penetration depth at very low temperatures related to the sub-gap quasiparticle spectrum. Dissipation of microwave power is predicted from intra- and inter- impurity band transitions at GHz frequencies at low temperatures, including a physical mechanism responsible for residual resistance. We predict anomalies in the resonant frequency, $f(T)$, and quality factor, $Q(T)$, of high-Q SRF cavities operating in the GHz range at low-temperatures that are sensitive to non-magnetic and paramagnetic impurity disorder. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_20565 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Microwave Response of Superconductors with Paramagnetic Impurities Zarea, Mehdi Sauls, J. A. Superconductivity We develop theoretical methods to predict the effects of paramagnetic impurities on the microwave response of conventional spin-singlet superconductors. Our focus is on superconducting devices and resonators with low concentrations of impurities and exchange interactions with conduction electrons. We connect the sub-gap quasiparticle spectrum generated by pair-breaking to the frequency and temperature dependence of the conductivity for superconductors operating at microwave frequencies. We report theoretical results for superconducting device performance -- dissipation, quality factor and frequency shift anomalies -- based on self-consistent calculations of the current response and penetraion of the electromagnetic field at the vacuum-superconducting interface. Key results include the prediction of a non-monotonic anomaly in the low-frequency superfluid fraction and penetration depth at very low temperatures related to the sub-gap quasiparticle spectrum. Dissipation of microwave power is predicted from intra- and inter- impurity band transitions at GHz frequencies at low temperatures, including a physical mechanism responsible for residual resistance. We predict anomalies in the resonant frequency, $f(T)$, and quality factor, $Q(T)$, of high-Q SRF cavities operating in the GHz range at low-temperatures that are sensitive to non-magnetic and paramagnetic impurity disorder. |
| title | Microwave Response of Superconductors with Paramagnetic Impurities |
| topic | Superconductivity |
| url | https://arxiv.org/abs/2512.20565 |