Nonlinear Dynamics in the Resonance Lineshape of NbN Superconducting Resonators

TL;DR

This paper investigates unusual low-power nonlinear dynamics in NbN superconducting resonators, revealing phenomena like resonance jumps and hysteresis, likely caused by local heating of weak links at grain boundaries.

Contribution

It presents the first detailed study of low-power nonlinear effects in NbN superconducting resonators and proposes a local heating hypothesis for the observed phenomena.

Findings

Nonlinear effects occur at significantly lower powers in NbN compared to Nb.

Resonance lineshape exhibits jumps, hysteresis, and frequency shifts.

Local heating of weak links likely causes the observed nonlinear dynamics.

Abstract

In this work we report on unusual nonlinear dynamics measured in the resonance response of NbN superconducting microwave resonators. The nonlinear dynamics, occurring at relatively low input powers (2-4 orders of magnitude lower than Nb), and which include among others, jumps in the resonance lineshape, hysteresis loops changing direction and resonance frequency shift, are measured herein using varying input power, applied magnetic field, white noise and rapid frequency sweeps. Based on these measurement results, we consider a hypothesis according to which local heating of weak links forming at the boundaries of the NbN grains are responsible for the observed behavior, and we show that most of the experimental results are qualitatively consistent with such hypothesis.