Josephson Coupling in the Dissipative State of a Thermally Hysteretic $\mu$-SQUID

TL;DR

This paper demonstrates that hysteretic $mbda$-SQUIDs can exhibit voltage oscillations due to supercurrent contributions surviving in the resistive state, enabled by efficient heat evacuation, allowing faster voltage read-out.

Contribution

It introduces a thermal and phase dynamics model explaining voltage oscillations in hysteretic $mbda$-SQUIDs, enabling their operation in a faster voltage read-out mode.

Findings

Voltage oscillations observed despite hysteresis.

Supercurrent persists deep into the resistive state.

Model accurately predicts flux modulation and retrapping current.

Abstract

Micron-sized superconducting interference devices ($\mu$-SQUIDs) based on constrictions optimized for minimizing thermal runaway are shown to exhibit voltage oscillations with applied magnetic flux despite their hysteretic behavior. We explain this remarkable feature by a significant supercurrent contribution surviving deep into the resistive state, due to efficient heat evacuation. A resistively shunted junction model, complemented by a thermal balance determining the amplitude of the critical current, describes well all experimental observations, including the flux modulation of the (dynamic) retrapping current and voltage by introducing a single dimensionless parameter. Thus hysteretic $\mu$-SQUIDs can be operated in the voltage read-out mode with a faster response. The quantitative modeling of this regime incorporating both heating and phase dynamics paves the way for further optimization of $\mu$-SQUIDs for nano-magnetism.