A long phase coherent normal (N) wire between superconductors (S) is characterized by a dense phase dependent Andreev spectrum . We probe this spectrum in a high frequency phase biased configuration, by coupling an NS ring to a multimode superconducting resonator. We detect a dc flux and frequency dependent response whose dissipative and non dissipative components are related by a simple Debye relaxation law with a characteristic time of the order of the diffusion time through the N part of the ring. The flux dependence exhibits h/2e periodic oscillations with a large harmonics content at temperatures where the Josephson current is purely sinusoidal. This is explained considering that the populations of the Andreev levels are frozen on the time-scale of the experiments.
@article{arxiv.1005.0406,
title = {Microwave response of an NS ring coupled to a superconducting resonator},
author = {F. Chiodi and M. Ferrier and K. Tikhonov and P. Virtanen and T. T. Heikkilä and M. Feigelman and S. Guéron and H. Bouchiat},
journal= {arXiv preprint arXiv:1005.0406},
year = {2019}
}