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Phenomenological Description of Microwave Characteristics of LowT_{c} Superconductor by ThreeFluid Model
Yoshio KOBAYASHI Hiromichi YOSHIKAWA Seiichiro ONO
Publication
IEICE TRANSACTIONS on Electronics
Vol.E80C
No.10
pp.12691274 Publication Date: 1997/10/25
Online ISSN: Print ISSN: 09168516 Type of Manuscript: Special Section PAPER (Special Issue on Basic Properties and Applications of Superconductive Electron Devices) Category: Keyword: lowT_{c} superconductors, microwave, surface impedance, conductivity,
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Summary:
It is shown that a threefluid model, which was successfully introduced to explain microwave characteristics of highT_{c} superconductors phenomenologically, is suit also to explain those of lowT_{c} superconductors. In this model, the two contributions of a residual normal electron, in addition to a super and a normal electron in the twofluid model, and of the temperature (T) dependence of momentum relaxation time τ for the two normal electrons are taken into account. Measured results of the T dependence of surface resistance R_{s} for a Nb film with critical temperature T_{c}9.2K agree very well with an R_{s} curve calculated using the present model, where a residual surface resistance at T0K, R_{s}o, and the T dependence of τ were determined using the surface reactance at 0K X_{s}o37.6mΩ calculated using the BCS theory to fit a calculated R_{s} curve with the measured values as a function of T. Furthermore, microwave characteristics predicted from the BCS theory cannot be explained phenomenologically using the conventional twofluid model. This difficulty can be solved by using an improved twofluid model, called the twofluid (τ) model, where the T dependence of τ is taken into account. Finally the frequency dependence of R_{s} calculated for the Nb film is f^{1.9} for the BCS theory and f^{2.0} for the threefluid (τ) model on the assumption of the frequency independence of τ.

