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  • Josephson junction  (1)
  • Tunneling spectroscopy  (1)
  • YBa2Cu3O7−x  (1)
  • high-T c superconductors  (1)
  • 1
    ISSN: 1572-9605
    Keywords: YBa2Cu3O7−x ; power handling ; magnetic and thermal field limitations ; defects ; microwave quenches
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Physical mechanisms which limit the power handling of YBa2Cu3O7−x films and devices are discussed in terms of a quantitative classification scheme. The possible limitations are devided into magnetic or thermal, and global or local in nature. Analytical estimations are compared with measurements of YBa2Cu3O7−x films (Ø = 1″–2″) using a niobium-shielded sapphire resonator at 19 GHz, and disk resonators at 2 GHz. Magnetic effects are found to play an essential role in nonoptimized films in terms of weak-links, and in high-quality films if the lower critical field Bcl is reached. The majority of films and disk resonators appear to suffer from microwave heating. Global heating appears predominantly at CW operation. Local heating results mainly from defects in films of medium quality. Defect-induced quenches are observed at moderate field levels, sometimes resulting in an irreversible degradation of the power handling.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 7 (1994), S. 361-365 
    ISSN: 1572-9605
    Keywords: Tunneling spectroscopy ; high-T c superconductors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Tunneling effects in YbBa2Cu3O7−x (YbBCO) and YbBa2Cu3O7−x (YBCO) single crystals have been investigated using an improved technique of break junction preparation. A two-gap structure with BCS-like density of states has been observed. The value of the “large” gap is in the range of 24–28 meV for YBCO (T c =85–90 K) and 29–30 meV for YbBCO (T c =87–90 K). A variation of the value of the “small” gap between 0.5 and 11 meV has been detected, even for the same crystal. As a possible explanation, two-band superconductivity, surface properties, or strong gap anisotropy will be discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9605
    Keywords: Microwave impedance ; microstrip resonator ; Josephson junction ; nonlinear power dissipation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The temperature, microwave current, and dc magnetic field dependencies of the effective surface resistanceR s of YBa2Cu3O7−x grain boundary Josephson junctions have been investigated at 6 GHz. The junctions were prepared on stepped LaAlO3 substrates and incorporated into tapered linear half-wavelength microstrip resonators. The characteristic parameters of the heterogeneous resonator were analyzed theoretically considering the junction as a lumped element of complex impedance. The microwave properties of the junction could then be extracted and related to their characteristic dc transport properties. The critical currentI c of the junction was found to limit the linear power dissipation in the superconducting strip. At microwave currents aboveI c , highly nonlinear microwave losses occurred, which displayed a characteristic magnetic field modulation. At even higher currents,R s saturated at a level corresponding to the normal resistanceR n of the junction.
    Type of Medium: Electronic Resource
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