Special CPM Seminar

Dynamics of Andreev states in a mesoscopic NS ring coupled to a superconducting resonator

Hélène Bouchiat

Laboratoire de Physique des Solides
Université Paris-Sud

A mesoscopic hybrid Normal/ Superconducting (NS) ring is characterized by an Andreev spectrum with a phase dependent minigap. We measure the linear response to a high frequency flux, in a wide frequency range, with a multimode superconducting resonator. We find that the current response contains, beside the well known dissipation-less Josephson contribution, a large dissipative component. At high frequency compared to the minigap and low temperature we find that the dissipation is due to transitions above the minigap. In contrast, at lower frequency there is range of temperature for which dissipation is caused predominantly by the relaxation of the Andreev states' population. This dissipative response, related via the fluctuation dissipation theorem to a non intuitive zero frequency thermal noise of supercurrent, is characterized by a phase dependence dominated by its second harmonic. It can be interpreted in terms of an effective dissipative conductance much larger than the classical Drude one.