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Surface-impedance measurements of superconducting NbN films

Technical Report ·
OSTI ID:5052776
The temperature and frequency dependences of the surface impedance of NbN thin films have been measured from 4.2 to 13 K and from 0.5 to 10 GHz using a stripline resonator. At 4.2 K resonant-cavity measurements of surface resistance were made at 35 and at 56 GHz. From surface reactance measurements using both cavity and stripline techniques, The authors obtain the penetration depth extrapolated to 0 K, gamma(0)=3700 {angstrom}. For the stripline, the film thickness was approximately 8000 {angstrom}, which is about two times the measured penetration depth. The weak-coupling Mattis-Bardeen theory was used to fit the temperature dependence of the surface resistance. Based on the quality of the weak-coupling fit to the data, they conclude that the strong-coupling effect is not important in the local and dirty limits. They discuss the correction due to the finite film thickness of the stripline measurements of the surface resistance.
Research Organization:
Massachusetts Inst. of Tech., Lexington, MA (United States). Lincoln Lab.
OSTI ID:
5052776
Report Number(s):
AD-A-235632/7/XAB; JA--6560; CNN: F19628-90-C-0002
Country of Publication:
United States
Language:
English