SKM 2023 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 63: Superconductivity: Theory

TT 63.14: Talk

Friday, March 31, 2023, 13:00–13:15, HSZ 103

Nonlinear response of diffusive superconductors to ac electromagnetic Fields — •Pascal Derendorf, Anatoly Volkov, and Ilya Eremin — Institut für Theoretische Physik III, Ruhr-Universität Bochum, Bochum, Germany

Using the generalized Usadel equation, we theoretically study the nonlinear response of a diffusive BCS superconductor to the action of electromagnetic fields. The response is found in the second order of the perturbation in the amplitude of the field E for the superconducting order parameter Δ and in the third order for the current j. We represent the matrix Keldysh function ĝ^K as the sum of a regular function ĝ^reg and an anomalous function ĝ^an . On the basis of this approach, general formulas for deviations of the retarded (advanced) Green’s functions, as well as the Keldysh function for an arbitrary number of harmonics of the incident field are explicitly obtained. The frequency and temperature dependencies of zero harmonic δ Δ ₀ (Eliashberg effect) and the second harmonic δ Δ _2Ω under action of a monochromatic irradiation are analyzed. We also study the third harmonic j_3Ω and the possibility of parametric amplification of a signal with a frequency Ω _x in the presence of a pumping with a frequency Ω which excites the Higgs (amplitude) mode.