ISSN:
1572-9605
Keywords:
High-temperature superconductivity
;
microwave cavities
;
sample surface impedance
Source:
Springer Online Journal Archives 1860-2000
Topics:
Electrical Engineering, Measurement and Control Technology
,
Physics
Notes:
Abstract We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR s of 1×1 cm2 superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE01δ oscillation mode the highly reproducible quality factor of about 105 results in a sensitivity of ±50μΩ forR s measurements. The temperature dependence ofR s can be measured up to values as high as 1 Ω. We have investigated several YBa2Cu3O7 thin films prepared by high oxygen pressure d.c. sputtering on LaAlO3 and NdGaO3. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivityρ(T) withρ(300K)/ρ(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT c , a further strong decrease ofR s at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForT≪Tc/2 these films exhibit an exp (−αT c/T) dependence ofR s withα-values around 0.4. These observations may be explained by a superconducting energy gap with 2Δ/kT c≈0.8 for charge carriers localized in the CuO chains for YBa2Cu3O7.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00618067
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