Accession Number : ADA260708

Title :   Microwave Studies of High Tc Copper Oxide Superconductors and NbN.

Descriptive Note : In-house rept.,

Corporate Author : ROME LAB HANSCOM AFB MA

Personal Author(s) : Chin, Chi-Chung

Report Date : NOV 1991

Pagination or Media Count : 96

Abstract : This report covers several projects, namely: surface impedance measurements using both stripline and cavity resonators; microwave magnetic field dependence measurements of the surface impedance of NbN; determination of the upper critical field of YBa2Cu3O7 by microwave measurements; and the calculation of the angular dependence of an anisotropic superconductor. The temperature and frequency dependencies of the surface impedance of NbN thin films were measured using a stripline resonator from 4.2 to 13 K and from 0.5 to 10 GHz. At 4.2 K resonant cavity measurements of the surface resistance were made at 35 and 56 GHz. From the surface reactance measurements using both cavity and stripline techniques, we obtain the penetration depth extrapolated to T=0 K. Lamba(0)=3700A. For the stripline, the film thickness was approximately 8000 angstrom, which is about twice the measured penetration depth. The weak-coupling (full) Mattis-Bardeen theory appropriate for NbN was used to fit the temperature dependence on the surface resistance. Based on the quality of the weak-coupling fit to the data, we conclude that the strong-coupling effect is not important in the local and dirty limits. The correction of the stripline measurements of the surface resistance due to the finite film thickness is discussed.

Descriptors :   *HIGH TEMPERATURE SUPERCONDUCTORS, *ANISOTROPY, *MICROWAVES, COPPER COMPOUNDS, THIN FILMS, MAGNETIC FIELDS, NIOBIUM COMPOUNDS.

Subject Categories : Electrical and Electronic Equipment
      Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE