Influence of resonances on the noise performance of SQUID susceptometers

TL;DR

This paper investigates how electromagnetic resonances affect the noise performance of SQUID susceptometers, developing a model to optimize their design for better signal-to-noise ratios.

Contribution

The study introduces a model that explains resonance effects on SQUID noise and demonstrates how damping resistors improve device performance.

Findings

Resonances significantly impact SQUID noise characteristics.

Damping resistors reduce resonances and improve flux noise performance.

Modeling helps optimize SQUID design for enhanced sensitivity.

Abstract

Scanning Superconducting Quantum Interference Device (SQUID) Susceptometry simultaneously images the local magnetic fields and susceptibilities above a sample with sub-micron spatial resolution. Further development of this technique requires a thorough understanding of the current, voltage, and flux characteristics of scanning SQUID susceptometers. These sensors often have striking anomalies in their current-voltage characteristics, which we believe to be due to electromagnetic resonances. The effect of these resonances on the performance of these SQUIDs is unknown. To explore the origin and impact of the resonances, we have developed a model that qualitatively reproduces the experimentally-determined current-voltage characteristics of our scanning SQUID susceptometers. We use this model to calculate the noise characteristics of SQUIDs of different designs. We find that the calculated ultimate flux noise is better in susceptometers with damping resistors that diminish the resonances than susceptometers without damping resistors. Such calculations will enable the optimization of the signal-to-noise characteristics of scanning SQUID susceptometers.