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IEEE Transactions on Applied Superconductivity

Shot noise in YBCO bicrystal Josephson junctions

K. Y. Constantinian, G. A. Ovsyannikov, I. V. Borisenko, J. Mygind, N. F. Pedersen

Published Jun 1, 2003• 5 citations
Publisher

Abstract

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.

DOI
10.1109/tasc.2003.813961

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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.
Detectors made from superconducting cuprate YBa/sub 2/Cu/sub 3/O/sub x/ bicrystal Josephson junctions (BJJs) on sapphire and NdGaO/sub 3/ substrates have been fabricated and characterized in the frequency band 200-900 GHz. Junctions on sapphire substrates had a normal state resistance R/sub N//spl ap/15-60 /spl Omega/, and I/sub C/R/sub N/ product up to 2.5 mV at T=4.2 K. Junctions on NdGaO/sub 3/ substrates had lower R/sub N/=1-5 /spl Omega/ and I/sub C/R/sub N/=0.4-0.9 mV at T=77 K. Three types of detecting devices have been investigated in both the broadband and the frequency-selective detection modes. One type was patterned with log-periodic antenna, and two others with Pt-metal double-slot antenna designed for a central frequency f=300 GHz and f=400 GHz, respectively. Measurements at f=320 GHz of the reception bandwidth /spl Delta/f for a device with double-slot antenna gave a quality factor Q=f//spl Delta/f/spl ap/10. A low-noise cooled 1-2 GHz bandwidth amplifier enables a better sensitivity in the self-pumping frequency mixing mode, avoiding the 1/f noise. The dependence of the spectral density of noise on voltage was compared to the data for the Josephson emission linewidth obtained by the selective detector response method. Also discussed are measurements at 500 GHz of the NEP values carried out at different experimental conditions.
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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.