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Conference on Precision Electromagnetic Measurements

Dependence of Josephson junctions arrays characteristics on temperature and frequency of microwave radiation

I. Ya. Krasnopolin

Published Dec 24, 2002• 0 citations
Publisher

Abstract

This paper presents the results of the measurements of 1-V Nb-AlO/sub x/-Nb, Josephson junctions arrays at temperatures 4.2-1.7 K in frequency band 54-80 GHz. The measurement of the temperature dependence of the critical current, gap voltage and subgap resistance of junctions is a useful tool for the quality control of arrays. By the measurements of the frequency dependence of array response to the microwave radiation it was found, that this response often has a resonance or interference like character, which is dependent on the array geometry. At the temperatures lower than 3-2.5 K as well as at low frequencies 54-60 GHz and T=4.2 K a transition to chaotic state of arrays was observed at small rf-power level.

DOI
10.1109/cpem.1996.547040

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This paper presents the results of the measurements of 1-V Nb-AlO/sub x/-Nb, Josephson junctions arrays at temperatures 4.2-1.7 K in frequency band 54-80 GHz. The measurement of the temperature dependence of the critical current, gap voltage and subgap resistance of junctions is a useful tool for the quality control of arrays. By the measurements of the frequency dependence of array response to the microwave radiation it was found, that this response often has a resonance or interference like character, which is dependent on the array geometry. At the temperatures lower than 3-2.5 K as well as at low frequencies 54-60 GHz and T=4.2 K a transition to chaotic state of arrays was observed at small rf-power level.
To investigate the temperature dependence of microwave-induced characteristics of a NbN Josephson junction array, the surface resistance, R/sub s/, of NbN films was measured using the dielectric resonator method at 22 GHz and temperatures from 5.8 K to 14.8 K. From the measured R/sub s/ values, the attenuation of 16 GHz microwaves in a NbN coplanar waveguide was calculated and constant-voltage-step amplitude for a NbN junction array biased with a DC current and 16 GHz microwaves was calculated as a function of temperature, resulting in a theoretical temperature dependence of constant-voltage-step amplitude.
We have measured the rf-bias-current dependence of the \ensuremath{\nu}/2 subharmonic spectral response of planar 300\ifmmode\times\else\texttimes\fi{}300 Nb-Au-Nb proximity-coupled Josephson-junction arrays. The \ensuremath{\nu}/2 subharmonic voltage spectrum was examined at two rf-bias frequencies, \ensuremath{\nu}/${\ensuremath{\nu}}_{\mathit{c}}$\ensuremath{\approxeq}1.4, 2.0 (${\ensuremath{\nu}}_{\mathit{c}}$\ensuremath{\approxeq}120 MHz), and in applied magnetic fields corresponding to f=0,1/2 flux quantum per plaquette. The measurements were compared to analytical predictions for an rf-biased asymmetric superconducting quantum interference device with non-negligble loop inductance and large rf-bias-current amplitudes, based on the resistively shunted Josephson-junction model. Reasonable agreement was found between experiment and theory, suggesting that a possible origin for the observed subharmonic behavior in arrays involves an interplay between array plaquette inductances and junction critical-current variations.
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