2025/12/12 by Khvalyuk, Anton V., Feigel'man, Mikhail V.
Materials Science · Physics and Astronomy · #Disordered Systems and Neural Networks (cond-mat.dis-nn) #Electronic and Structural Properties of Oxides #FOS: Physical sciences #Iron-based superconductors research #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #Physics of Superconductivity and Magnetism #Superconductivity (cond-mat.supr-con)
paper · doi:10.48550/arxiv.2512.11636
openalex publication_date 2025/12/12 · openalex created_date 2025/12/16 · openalex updated_date 2026/07/28
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 ΔP both below and above the transition temperature Tc. We develop a novel microscopic theory of the dependence of 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 ℏω, T≪Δ≤ΔP, where Δ is the typical superconducting order parameter, distinct from ΔP. 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≪ Tc. Our theory provides a microscopic understanding of existing and future experiments on thin films of InOx, 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.