Unusual nonlinear dynamics observed in NbN superconducting microwave resonators

Abstract

We report on some unusual nonlinear dynamics observed in several NbN superconducting stripline microwave resonators. Among the nonlinear effects observed: abrupt bifurcations within the resonance lineshape, hysteretic behavior, hysteresis loops changing direction, resonance shift and critical coupling. Weak links forming at the boundaries of the columnar structure of the NbN films are hypothesized as the main origin of the nonlinearities. © 2006 IOP Publishing Ltd.