We describe theoretically the depairing effect of a microwave field on diffusive s-wave superconductors. The ground state of the superconductor is altered qualitatively in analogy to the depairing due to a dc current. In contrast to dc-depairing the density of states acquires, for microwaves with frequency ω0, steps at multiples of the photon energy Δ±nℏω0 and shows an exponential-like tail in the subgap regime. We show that this ac-depairing explains the measured frequency shift of a superconducting resonator with microwave power at low temperatures.
@article{arxiv.1603.02726,
title = {Coherent excited states in superconductors due to a microwave field},
author = {A. V. Semenov and I. A. Devyatov and P. J. de Visser and T. M. Klapwijk},
journal= {arXiv preprint arXiv:1603.02726},
year = {2016}
}