Superconductivity in the presence of microwaves: Full phase diagram

TL;DR

This paper refines Eliashberg theory to analyze how microwave irradiation affects superconductivity, revealing regions of stimulation and suppression depending on temperature and frequency, and examining supercurrent behavior.

Contribution

It generalizes the Eliashberg theory to arbitrary temperatures and frequencies, providing a detailed phase diagram of microwave effects on superconductivity.

Findings

Microwave radiation can stimulate superconductivity in specific $(\omega,T)$ regions.

Superconductivity is suppressed by weak microwave driving at low temperatures and high frequencies.

The study establishes criteria for supercurrent enhancement under microwave irradiation.

Abstract

We address the problem of non-equilibrium superconductivity in the presence of microwave irradiation. We refine the old Eliashberg theory and generalize it to arbitrary temperatures $T$ and frequencies $\omega$. Microwave radiation is shown to stimulate superconductivity in a bounded region in the $(\omega,T)$ plane. In particular, for $T<0.47\, T_c$ and for $\hbar\omega>3.3\, k_BT_c$ superconductivity is always suppressed by a weak \emph{ac} driving. We also study the supercurrent in the presence of microwave irradiation and establish the criterion for the critical current enhancement. Our results can be qualitatively interpreted in terms of the interplay between the kinetic ("stimulation" vs. "heating") and spectral ("depairing") effects of the microwaves.