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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Submillimeter wave response and noise in HTS Josephson junctions

Michael A. Tarasov, A. Shul’man, O. Y. Polyansky, Z. G. Ivanov, Georg Fischer, E. Kollberg, T. Claeson, Е. А. Степанцов

Published Dec 18, 1996• 0 citations
Publisher

Abstract

The IV curves and the direct detector response of HTS bicrystal grain-boundary Josephson junctions have been measured under submm-wave irradiation at frequencies 350-750 GHz. The Josephson oscillation spectrum has been measured using the Hilbert transformation of detection response dependence. The Josephson oscillation linewidth and corresponding value of effective noise is compared to the estimates from the dc measurements of noise rounding of IV curve. To separate sources of noise the direct measurements of junction's output noise has been performed at 1.5 GHz and low frequencies 0.5-20 kHz.

DOI
10.1117/12.262784

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The IV curves and the direct detector response of HTS bicrystal grain-boundary Josephson junctions have been measured under submm-wave irradiation at frequencies 350-750 GHz. The Josephson oscillation spectrum has been measured using the Hilbert transformation of detection response dependence. The Josephson oscillation linewidth and corresponding value of effective noise is compared to the estimates from the dc measurements of noise rounding of IV curve. To separate sources of noise the direct measurements of junction's output noise has been performed at 1.5 GHz and low frequencies 0.5-20 kHz.
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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.