Coherent Excited States in Superconductors due to a Microwave Field
A. V. Semenov (Moscow Institute of Physics and Technology, Moscow State Pedagogical University)
I. A. Devyatov (Moscow State University, Moscow Institute of Physics and Technology)
P. J.de Visser (SRON–Netherlands Institute for Space Research, TU Delft - QN/Klapwijk Lab)
Teun M. Klapwijk (Moscow State Pedagogical University, TU Delft - QN/Klapwijk Lab)
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Abstract
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±n ω0 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.