Dissipation due to bulk localized low-energy modes in strongly disordered superconductors
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arXiv
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| Format: | Preprint |
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2025
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| author | Khvalyuk, Anton V. Feigel'man, Mikhail V. |
| author_facet | Khvalyuk, Anton V. Feigel'man, Mikhail V. |
| contents | Strongly disordered superconductors (SDSCs) are widely used in qubits, microwave resonators, photon detectors, and other superconducting quantum devices. In SDSC-based devices, coherence times are limited by low-temperature microwave dissipation in the material. However, the standard Mattis--Bardeen theory fails in SDSCs because their single-particle spectrum exhibits a hard pseudogap $Δ_{P}$ both below and above the transition temperature $T_{c}$. We develop a novel microscopic theory of the dependence of \emph{ac }dissipation in such systems on temperature $T$ and frequency $ω$. We analyze the resonator quality factor $Q(ω,T)$ in the practically relevant range $\hbarω,\,T\llΔ\leqΔ_{P}$, where $Δ$ is the typical superconducting order parameter, distinct from $Δ_{P}$. We show that low-$ω$ dissipation is dominated by a new type of bulk localized collective modes arising from spatial inhomogeneity of the superconducting state. Consequently, $Q(ω)$ decreases strongly with $ω$ and exhibits two-level-system-like growth with $T$ for $T\ll T_{c}$. Our theory provides a microscopic understanding of existing and future experiments on thin films of $\mathrm{InO}_{x}$, TiN, NbN, and similar SDSCs, and is phenomenologically relevant to granular aluminum films. The results suggest strategies to mitigate intrinsic microwave losses in SDSC-based quantum devices. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_11636 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Dissipation due to bulk localized low-energy modes in strongly disordered superconductors Khvalyuk, Anton V. Feigel'man, Mikhail V. Superconductivity Disordered Systems and Neural Networks Mesoscale and Nanoscale Physics Strongly disordered superconductors (SDSCs) are widely used in qubits, microwave resonators, photon detectors, and other superconducting quantum devices. In SDSC-based devices, coherence times are limited by low-temperature microwave dissipation in the material. However, the standard Mattis--Bardeen theory fails in SDSCs because their single-particle spectrum exhibits a hard pseudogap $Δ_{P}$ both below and above the transition temperature $T_{c}$. We develop a novel microscopic theory of the dependence of \emph{ac }dissipation in such systems on temperature $T$ and frequency $ω$. We analyze the resonator quality factor $Q(ω,T)$ in the practically relevant range $\hbarω,\,T\llΔ\leqΔ_{P}$, where $Δ$ is the typical superconducting order parameter, distinct from $Δ_{P}$. We show that low-$ω$ dissipation is dominated by a new type of bulk localized collective modes arising from spatial inhomogeneity of the superconducting state. Consequently, $Q(ω)$ decreases strongly with $ω$ and exhibits two-level-system-like growth with $T$ for $T\ll T_{c}$. Our theory provides a microscopic understanding of existing and future experiments on thin films of $\mathrm{InO}_{x}$, TiN, NbN, and similar SDSCs, and is phenomenologically relevant to granular aluminum films. The results suggest strategies to mitigate intrinsic microwave losses in SDSC-based quantum devices. |
| title | Dissipation due to bulk localized low-energy modes in strongly disordered superconductors |
| topic | Superconductivity Disordered Systems and Neural Networks Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2512.11636 |