Theory of disordered superconductors with applications to nonlinear current response

Journal Article · 21 February 2022 · Progress of Theoretical and Experimental Physics

DOI: https://doi.org/10.1093/ptep/ptac034 · OSTI ID:1846812

Sauls, J. A.  ^[1]

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1. Northwestern Univ., Evanston, IL (United States)

I present a review of the theory and basic equations for charge transport in superconducting alloys starting from the Keldysh formulation of the quasiclassical transport equations developed by Eilenberger, Larkin and Ovchinnikov, and Eliashberg. This formulation is the natural extension of Landau’s theory of normal Fermi liquids to the superconducting state of strongly correlated metals. For dirty metals the transport equations reduce to equations for charge diffusion, with the current response given by the Drude conductivity at low temperatures. The extension of the diffusion equation for the charge and current response of a strongly disordered normal metal to the superconducting state yields Usadel’s equations for the nonequilibrium quasiclassical Keldysh propagator. The conditions for the applicability of the Usadel equations are discussed, the pair-breaking effect of disorder on the current response, including the nonlinear current response to an electromagnetic field in the dirty limit, τ ≪ ℏ/Δ, are reported. The same nonlinearity is shown to lead to source currents for photon generation and nonlinear Kerr rotation driven by the nonlinear response to excitation of the superconductor by a multi-mode electromagnetic field. The potential relevance of the nonlinear source currents to superconducting radio-frequency cavities as detectors of axion-like dark matter candidates is briefly discussed.

• Research Organization: Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)
• Sponsoring Organization: USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: AC02-07CH11359
• OSTI ID: 1846812
• Report Number(s): FERMILAB-PUB-22-060-SQMS-V; arXiv:2202.02260; oai:inspirehep.net:2027771; TRN: US2303048
• Journal Information: Progress of Theoretical and Experimental Physics, Vol. 2022, Issue 3; ISSN 2050-3911
• Publisher: Physical Society of JapanCopyright Statement
• Country of Publication: United States
• Language: English