Microwave response of an NS ring coupled to a superconducting resonator

F. Chiodi, M. Ferrier, K. Tikhonov, P. Virtanen, T. T. Heikkilä, M. Feigelman, S. Guéron, H. Bouchiat

Published 2010-05-03, updated 2011-11-10Version 2

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.