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Journal of Radio Electronics

Features of the spectrum of a niobium Josephson junction array measured with the use of high-Tc Josephson mixer

Mikhail A. Galin, A. I. El’kina, M. Yu. Levichev, Д.В. Мастеров, Alexey E. Parafin, L. S. Revin

Published Feb 1, 2025• 0 citations
Publisher

Abstract

Spectral measurements of a niobium Josephson junction arrays with overwavelength dimensions have been performed using a heterodyne receiver with a mixer based on a high-Tc bicrystal transition. The array is fabricated on a silicon substrate and is composed from 9996 series connected Nb/NbSi/Nb junctions embedded to parallel single-strip lines with the length 7.1 mm. The mixer in the receiver is a Josephson junction formed by a YBaCuO film on a bicrystal boundary of Zr1−xYxO2 substrate. Spectral measurements have been performed in the frequency ranges 150-180 GHz and 225-250 GHz. The aim of the work was the investigation of the influence to the spectral line from some factors of external electrical circuit: the type of power supply and the level of technical noises. Significant decrease of the linewidth from ~ 10 MHz to 0.5-0.8 MHz has been found at the connection of the array to voltage source instead of current source and at the minimizing of technical noises. The shift of spectral frequency from the Josephson one averaged over the array has been observed that is explained by the peculiarities of synchronization of Josephson junctions in large arrays.

DOI
10.30898/1684-1719.2025.2.4

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Spectral measurements of a niobium Josephson junction arrays with overwavelength dimensions have been performed using a heterodyne receiver with a mixer based on a high-Tc bicrystal transition. The array is fabricated on a silicon substrate and is composed from 9996 series connected Nb/NbSi/Nb junctions embedded to parallel single-strip lines with the length 7.1 mm. The mixer in the receiver is a Josephson junction formed by a YBaCuO film on a bicrystal boundary of Zr1−xYxO2 substrate. Spectral measurements have been performed in the frequency ranges 150-180 GHz and 225-250 GHz. The aim of the work was the investigation of the influence to the spectral line from some factors of external electrical circuit: the type of power supply and the level of technical noises. Significant decrease of the linewidth from ~ 10 MHz to 0.5-0.8 MHz has been found at the connection of the array to voltage source instead of current source and at the minimizing of technical noises. The shift of spectral frequency from the Josephson one averaged over the array has been observed that is explained by the peculiarities of synchronization of Josephson junctions in large arrays.
We performed spectral measurements of a large niobium Josephson junctions array. The array consists of 9996 serially connected Nb/NbSi/Nb junctions placed on a 1×1 cm silicon substrate. The spectrum was analyzed by a heterodyne superconducting receiver based on a high-TcJosephson mixer. It was discovered that the linewidth of Josephson radiation is strongly influenced by configuration and type of a measurement system. We obtain the linewidth down to 0.2 MHz when connecting the array to an autonomous power source and minimizing technical noise. We also observed the shift of the spectral frequency from the Josephson one that can be explained by peculiarities of synchronization of such large multi-oscillator systems.
We performed the spectral measurements of a niobium based Josephson junction array in order to estimate the linewidth of Josephson emission. The array is formed by 9996 serially connected Nb/NbSi/Nb Josephson junctions occupying the area of 5×7 mm2on a silicon substrate and divided into 7 distinct subarrays. The array was immersed in a liquid helium dewar from where the emission was brought to open space via an oversize waveguide. Firstly, the measurements on a Fourier-transform spectrometer were carried out in a wide frequency range 139–343 GHz at almost all self-induced steps of current-voltage curve. As in our previous work, the observed linewidth of Josephson emission corresponded to the resolution of the spectrometer. Then, we carried out more precise and sensitive measurements using the 211–275 GHz heterodyne receiver based on a Nb/AlOx/Nb mixer with a spectral resolution better than 0.1 MHz. Dependencies of the linewidth on the step number and on the number of connected subarrays are studied. The peaks corresponding to the 2ndharmonic of the Josephson generation are also observed in the spectra. The linewidth of the main harmonic down to 1.5 MHz was observed in these measurements.
We report heterodyne measurements of Josephson microwave radiation emitted by a parallel array of small superconductor-insulator-superconductor (SIS) junctions at submillimeter-wave frequencies. The array consists of five Nb/Al–AlOx/Nb junctions nonevenly distributed in a niobium superconducting stripline, and is optimized for rf coupling in the 450–640 GHz range. We observed Fiske-like resonant steps in its I-V curve in the presence of magnetic field. The device was placed in a waveguide mount, and its radiation was quasioptically coupled out of the cryostat, to a SIS-mixer spectrometer in the same frequency range, with a 4–8 GHz band for spectral analysis. We detected a coherent signal in the spectra when the array was biased on the first and third steps, respectively, at the first harmonic frequency of 242 GHz and at the fundamental frequency of 493 GHz, both being the Josephson frequencies associated with their dc voltages. This strongly suggests that this type of parallel arrays optimized for wideband rf coupling, though strongly discretized, hosts dynamic fluxon regimes similar to long Josephson junctions, which could find applications in superconducting digital electronics or integrated heterodyne submillimeter-wave receivers.
We measured spectral noise density in YBCO symmetric bicrystal Josephson junctions on sapphire substrates at bias voltages up to 100 mV and T=4.2 K. Normal state resistance of the Josephson junctions, R/sub N/=20-90 /spl Omega/ and I/sub C/R/sub N/ up to 2.2 mV have been observed in the experimental samples. Noise measurements were carried out within frequency bands of 1-2 GHz and 0.3-300 kHz. At bias voltages 10/spl les/V/spl les/60 mV a linear voltage dependence of noise power has been registered, while at V/spl les/5 mV a noticeable noise rise has been observed. The latter may explain the experimentally measured linewidth broadening of Josephson oscillations at mm and submm wave frequencies in high-Tc superconducting junctions. Experimental results are discussed in terms of bound states existing at surfaces of d-wave superconducting electrodes.
We report the millimeter wave mixing properties of high-T c superconductor Josephson junction arrays using a waveguide-to-microstrip converter in the 100 GHz frequency range. The junction arrays consist of 3 weak links fabricated from EuBa2Cu3O7-δ thin films grown on an MgO bicrystal substrate. In these junction arrays, Shapiro steps are observed in the presence of 100 GHz irradiation at intervals of 3 times the fundamental step voltage. Millimeter wave mixing with an input local oscillator frequency of 99.142 GHz and an input signal frequency of 99.880 GHz is detected as the IF output at 738 MHz. The IF output power peaks at voltages corresponding to those of the dynamic resistance dV/ dI. A mixing conversion efficiency of -24.1 dB is obtained for a 3-junction array.
Josephson junction arrays could be competitive candidates for radiation sources in the frequency range from 0.5 to 1.5 THz. This is the range where compact solid-state continuous wave sources are most lacking. We investigated the millimeter-wave radiation from arrays of high-temperature superconductor bicrystal Josephson junctions embedded in a quasi-optical resonator. The novel approach of utilizing the intrinsic resonance modes of the substrate to improve the impedance coupling between the series array of discrete Josephson junctions and the quasi-optical resonator was investigated by experiments and electromagnetic field simulations. Radiation from the arrays containing up to 536 junctions was detected at about 80 GHz and liquid nitrogen temperature using a low-noise receiver. The detected maximum radiation power of the arrays was about 50 pW and the peak voltage agreed exactly with the Josephson current–voltage relation.