Asymmetric voltage noise in superconducting tunnel junctions with electromagnetic environment

TL;DR

This paper provides a theoretical analysis of voltage noise and hysteresis in superconducting tunnel junctions, revealing how electromagnetic environment influences these phenomena and explaining experimental anomalies.

Contribution

It introduces a matrix-continued-fraction method to analyze voltage noise and hysteresis, highlighting the environmental effects on superconducting junction behavior.

Findings

Voltage noise shows asymmetry between forward and backward current ramps.

Hysteresis and noise anomalies are due to electromagnetic environment effects.

Discontinuous changes in noise occur near the switching current.

Abstract

We investigate theoretically the V-I characteristics and voltage noise of superconducting tunnel junctions with small critical current via the matrix-continued-fraction method. Special attention is paid to the large hysteresis in the V-I characteristics and to the voltage-noise anomaly observed in preliminary experiments. The current dependence of the voltage noise shows a strong asymmetry between the forward and backward current ramping and a discontinuous change of the noise close to its measured maximum occurring at the switching current. We show that both the large hysteresis and the voltage noise anomaly in this current-biased setup are a consequence of the influence of junction's electromagnetic environment. Typically, the voltage-noise dependence on the junction current parametrized by the external drive contains a loop which is, however, not observed experimentally because of the implementation of the junction-current ramp. Skipping a part of the loop is responsible for the observed hysteresis as well as the noise anomaly.