Thermal Instability and Self-Sustained Modulation in Superconducting NbN Stripline Resonators

We study theoretically and experimentally the response of a microwave superconducting stripline resonator, integrated with a microbridge, to a monochromatic injected signal. We find that there is a certain range of driving parameters, in which a novel nonlinear phenomenon immerges, and self-sustained modulation of the reflected power off the resonator is generated by the resonator. A theoretical model which attributes the self modulation to a thermal instability yields a good agreement with the experimental results.