Presentation Information
[16a-PA1-9]Nonlinear Electromagnetic Response and Nonlinear RF Losses in Superconductors: Direct nonlinear Photon Contributions, Eliashberg Effect, and the Higgs Mode
〇Takayuki Kubo1,2 (1.KEK, 2.Sokendai)
Keywords:
superconductivity,nonlinear,dissipation
It is known that the quality factor Q of superconducting resonators depends on the microwave field amplitude A (i.e., Q(A)), and that, as the frequency increases, the amplitude dependence can switch from a decreasing to an increasing function, while a firm theoretical understanding is still lacking. In this work, based on the microscopic theory of nonequilibrium superconductivity (the Keldysh-Usadel formalism), we derive nonlinear corrections to the complex conductivity by performing a nonequilibrium perturbative expansion up to third order in A. In the low-temperature and low-frequency regime, the contributions from the Eliashberg effect and Higgs-mode oscillations are found to be small, and the direct nonlinear photon (AAA) term dominates the nonlinear loss correction delta sigma_1. We further show that the high-frequency inversion of Q(A) originates from the same AAA contribution. [Physica Review Applied 24, 064061 (2025)]