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Microwave Characteristics of HighT_{c} Superconductors by Improved ThreeFluid Model
Tadashi IMAI Takaaki SAKAKIBARA Yoshio KOBAYASHI
Publication
IEICE TRANSACTIONS on Electronics
Vol.E76C
No.8
pp.12751279 Publication Date: 1993/08/25
Online ISSN: Print ISSN: 09168516 Type of Manuscript: Special Section PAPER (Special Issue on HighTemperature Superconducting Electronics) Category: Keyword: highT_{c} superconductor, microwave, dielectric resonator, complex conductivity, momentum relaxation time, improved threefluid model,
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Summary:
In order to explain the temperature and frequency characteristics of highT_{c} superconductors, a new model is proposed, which will be called the improved threefluid model, where the momentum relaxation time τ is assumed to depend on temperature in the superconducting and normal states, respectively, although τ has been assumed to be independent of temperature for the conventional threefluid model. According to this model, the complex conductivity σ_{1}jσ_{2} and the surface impedance Z_{s}R_{s}jX_{s}, where R_{s} is the surface resistance and X_{s} is the surface reactance, are expressed as a function of temperature. The temperature dependences of Z_{s} and for a YBCO bulk estimated using this model agree very well with ones measured by the dielectricloaded cavity method in room to cryogenic temperature. In particular, a peak of σ_{1} observed just below the critical temperature T_{c} in experiments, appeared in the calculated results based on this model. This phenomenon has been already known in the BCS theory. Thus, it is verified that this model is useful to explain the microwave characteristics of highT_{c} superconductors in room to cryogenic temperature. On the other hand, the residual normal electron density n_{res}4.25410^{23} m^{3} and the total electron density n_{t}7.30810^{24} m^{3} are obtained by calculation. The ratio n_{res}/n_{t}0.058 can be used as figure of merit to evaluate material quality of highT_{c} superconductors; thus it means that there is 5.8% nonpairing electron in this YBCO bulk.

