Mesoscopic SNS junctions and their application to SQUIDs and millimeter-wave detectors |
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| Institution: | 1. School of Physics, Beijing Institute of Technology, Beijing, 100081, China;2. College of Physics and Energy, Shenzhen University, Shenzhen, 518060, China;3. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic Systems, School of Physics, Beijing Institute of Technology, Beijing, 100081, China;4. Shanghai Key Laboratory of High Temperature Superconductors, International Center of Quantum and Molecular Structures, Department of Physics, Shanghai University, Shanghai, 200444, China;1. Department of Physics Education, Chosun University, Gwangju, 61452, South Korea;2. Department of Physics, Chonbuk National University, Jeonju, 54896, South Korea;3. Center for Theoretical Physics of Complex Systems, Institute for Basic Science, Daejeon, 34126, South Korea;4. Basic Science Program, Korea University of Science and Technology(UST), Daejeon, 34113, South Korea;1. Plasma Physics Research Center, Science and Research Branch, Islamic Azad University, Tehran, Iran;2. Department of Physics, Tehran Payame Noor University (PNU), P.O. Box 19395-3697 Tehran, Iran;1. Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA |
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| Abstract: | Mesoscopic SNS junctions have been studied both in the ballistic and diffusive regimes. SNS junctions in the ballistic regime behave as an ideal Fermion oscillator which is to be compared with the Boson oscillator or the Planck theory of blackbody radiation. The current of mesoscopic SNS junctions in the diffusive regime has the same phase dependence as that of dirty-limit short weak links derived by a transport equation. Recent theories of mesoscopic SNS junctions have successfully unified the theories of the tunnel Josephson junction, the clean-limit short weak link and the dirty-limit short weak link which look very different conceptionally. We can even observe transitions among the three types of junctions when we change the transmission coefficients of the barriers between the superconducting electrodes experimentally. We looked experimentally for the optimum transmission coefficient which gives the minimum low-frequency telegraph noise in order to make a low-noise SQUID magnetometor for brain science. We have observed signals of 5 fT from human brains with a good signal-to-noise ratio using the SQUID magnetometor of the SNS junctions. The 64-channel SQUID magnetometer of SNS junctions has confirmed that mesoscopic SNS junctions are important not only theoretically but also practically. These data could encourage people studying SNS junctions of high-Tc superconductors. |
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