Effects of Nonmagnetic Impurities on Nonequilibrium Phase Transitions in Microwave-Driven Superconductors
Year: 2026
Type: preprint
Abstract: We investigate the nonequilibrium steady states of a microwave-driven BCS superconductor in the presence of nonmagnetic impurity scattering and energy relaxation. Using the Floquet-Nambu-Keldysh Green's function method together with the self-consistent Born approximation, we self-consistently determine the superconducting order parameter in the microwave-driven steady state. We find that the nonequilibrium phase diagram depends strongly on the impurity-scattering strength. When impurity scattering is absent or weak, the steady-state order parameter is single-valued at each temperature and drive frequency. At intermediate scattering strengths, we find bistability between microwave-enhanced and microwave-suppressed superconducting states. As the impurity-scattering strength increases further, we instead find bistability between the superconducting and normal states. This evolution reflects competition between two effects of microwave driving: Eliashberg-type enhancement through the redistribution of thermally excited quasiparticles and suppression through pair-breaking-induced quasiparticle generation. In contrast to the robustness of equilibrium $s$-wave superconductivity against nonmagnetic impurity scattering, our results demonstrate that nonmagnetic impurity scattering plays a central role in determining the character of nonequilibrium superconducting phase transitions under microwave driving.
Source: arXiv (Cornell University)
Author: Kawamura, Taira
Institution: Nihon University
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G8694808977
OpenAlex ID: W7223007470