Self-induced Structure in the Current-Voltage Characteristics of RSQUIDs

Colin M Pegrum and John C Macfarlane

Abstract—Resistive two-junction SQUIDs (RSQUIDs) made from high-temperature superconductors are being developed as narrow-line width tunable oscillators in the GHz frequency range. We present here the results of numerical simulation of RSQUIDs of this type. These studies have identified conditions where sub-harmonic steps and other features are apparent in the current-voltage characteristics, driven by the internally-generated heterodyne frequency. The behavior is sensitive to the frequency (set by the voltage across the resistive element in the RSQUID), the temperature and also the loop inductance. We have studied the effects of thermalnoise on these features. We also assess how these effects might be observed,and consider how they might affect practical applications of high frequency heterodyne RSQUID oscillators.

IndexTerms—Superconducting devices, SQUIDs, Josephson oscillators, heterodyning.

Manuscript received 19 August 2008.
ColinPegrum is with Field Solutions, Glasgow G12 9SD and also
with the Department of Physics, University of Strathclyde, Glasgow G4 0NG, UK
(e-mail: fieldsolu-tions@colinpeg2.plus.com).
John Macfarlane is with the Department of Physics, University of Strathclyde, Glasgow G4 0NG,
UK (e-mail:j.c.macfarlane@strath.ac.uk).

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