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Japanese Journal of Applied Physics

Average Voltage Measurements of Periodic Blocking Oscillation in Resistive Superconducting Quantum Interference Device Connected to Josephson Transmission Line

Yoshinao Mizugaki

Published Feb 17, 2012• 1 citation
Publisher

Abstract

Blocking oscillation (BO) is a unique operation mode of resistive superconducting quantum interference devices (RSQUIDs). The author presents experimental measurements of periodic BO by means of the average voltage method. Test circuits are fabricated using a Nb/AlO x /Nb integration process. The input/output voltage ratio in an RSQUID, of which the output is connected to a Josephson transmission line (JTL), becomes 2 under appropriate operation conditions. Since the voltage ratio is exactly proportional to the input/output switching frequency ratio, the results demonstrate the periodic BO, in which the numbers of switching during one period are 2 and 1 in the input and output junction, respectively.

DOI
10.1143/jjap.51.038001

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Partly resistive superconducting quantum interference devices (RSQUIDs) are used in noise thermometry in the liquid helium temperature range. Here we analyze one type of RSQUID that has not been thoroughly investigated until now: the direct current biased with two Josephson junctions and a resistive part connected in series with the junctions and closed by a superconducting ring. The resistive shunted model of the Josephson junctions is used for the analysis. Two cases of the RSQUID ring inductance were analyzed: (i) negligibly small and (ii) small but finite inductance. The expressions for the low frequency output signal, the current–voltage (I–V) characteristics, and the current flowing through the resistive part are obtained. In the dependence of the output frequency versus the dc current passed through the resistive part often an offset is observed experimentally. This phenomenon can be explained as an influence of an asymmetry in the critical currents of the junctions.
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