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 emerges, 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.