Surface resistance measurement of superconducting YBa 2 Cu 3 O 7 in a magnetic field
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P. J. Rainville, A. J. Drehman, J. S. Derov, and J. Steinbeck Rome Air Development Center (RADC), Hanscom AFB, Massachusetts 01731-5000
G. Dresselhausb) Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
M. S. Dresselhaus Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 9 November 1989; accepted 3 May 1990)
We report on the magnetic-field dependent surface resistance of polycrystalline YBa2Cu3O7 (Tc — 92 K), measured using a brass cylindrical cavity resonator, operating at 16.5 GHz in the TEOU mode. A dc magnetic field // app is applied parallel to the superconducting sample surface, and the temperature dependence of the surface resistance is measured for four different values of H^v (0 T, 0.22 T, 1 T, 5 T). An effective medium theory and the two-fluid model are used to fit the surface resistance versus temperature measurements both in zero field and for various applied fields. These results are applied to characterize the microwave properties of a polycrystalline ceramic superconductor.
I. INTRODUCTION
The microwave properties of superconductors are important for scientific reasons to enable study of the electromagnetic response of a superconductor for frequencies near but below the superconducting gap and temperatures below Tc. The nonvanishing values of the surface resistance under these conditions further allow exploration of the effect of an external magnetic field on the electromagnetic response. From a practical standpoint, the surface resistance of a superconductor suggests use of superconductors in microwave resonant cavities to achieve very high Q values. The high Tc superconductors open up such possibilities in the liquid nitrogen temperature range. The temperature dependence of surface resistance is an important quantity for describing the microwave properties of high Tc materials. The surface resistance, RS(T), can be described as a sum of Rth{T) + RKS, where Rth{T) is the intrinsic temperature dependent surface resistance and Rres is the residual surface resistance and is measured to be relatively independent of temperature. In this paper the temperature dependence of R,h{T) is examined as a means to characterize polya)
Visiting scientist at RADC. Visiting scientist at RADC under the AFSC University Residence Research Program.
b)
J. Mater. Res., Vol. 5, No. 8, Aug 1990
http://journals.cambridge.org
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crystalline ceramic samples, providing information on the temperature and magnetic field dependence of the characteristic parameters: the penetration depth A, the fraction of the sample that is superconducting, and the residual surface resistivity. We assume that a fraction of the polycrystalline ceramic sample consists of nonsuperconducting components, and we use an effective medium approximation1 and the two-fluid model to calculate RS{T) over the whole temperature range of interest. A fit of the
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