Microwave Surface Resistance Measurements Research Articles

Cryogenic system for measurements of microwave surface resistance. Application to high-Tc superconductors

A simple experimental set-up for the measurement of the microwave surface resistance in the temperature range 20-300 K is described. The microwave setup consists of a Gunn generator, a set of standard Hewlett Packard microwave components and a cylindrical resonant cavity. The measurement technique is presented and applied to the study of the resistive transition of high-temperature superconductors.

Microwave surface resistance and power dependence of thallium-based films deposited onto large-area silver substrates

Microwave surface resistance (R s ) measurements on large-area (11.4 cm2) Tl-based films deposited onto Ag (Consil 995) substrates have been made at a frequency of 18 GHz as a function of temperature. Deposition onto unoriented Ag substrates yields unoriented films characterized byR s values of 8.2 and 33.6 mΩ at 10.6 and 77 K, respectively. In contrast, similar deposition onto oriented Ag substrates yields oriented films with values of 12.6 and 14.6 mΩ at 11.2 and 77 K, respectively; corresponding Cu values are 9 and 21 mΩ. Additionally, it is found that the dependence ofR s on microwave surface magnetic fieldH s is weaker for the oriented films. These results suggest that the effect of orienting thec-axis in Tl films is twofold: (1) the high-frequency superconducting transition is made considerably sharper, resulting in a lowerR s value at 77 K, and (2) the rate of increase inR s with appliedH s is reduced. Both effects have significant ramifications for the potential application of these materials to high-frequency accelerating cavities.

Measurement of microwave surface resistance of patterned superconducting thin films

A simple and versatile measurement technique has been demonstrated for characterization of thin film superconductors and the substrates on which they are deposited. Unlike other state of the art measurements that characterize only the top layer of unpatterned thin films in end-plate replacement or perturbation-type cavity arrangements, we test the sample under conditions very close to those of actual microwave circuit applications. Measurements on a laser deposited, thin-film YBCO superconductor, patterned in the form of a meander line on a LaAlO3 substrate, show a microwave surface resistance one order of magnitude lower than that of copper at 79 K and 11 GHz. At 1.4 GHz and 79 K, an improvement by over two orders of magnitude is observed. This is the first demonstration of superior microwave performance of a comb filter structure using a HTS thin film.

Microwave surface resistance in Tl-based superconducting thin films

We report measurements of microwave surface resistance in Tl-based superconductor thin films made by laser ablation followed by a post-deposition thermal process. The films were measured by using cavity methods. The data at 9.5 and 148 GHz indicate that the residual resistance scales as f2. At 77 K, the 9.5 GHz surface resistance is ten times smaller than oxygen-free high-conductance copper at the same temperature and frequency. The 9.5 GHz measurement also indicates that the film-substrate interface does not cause more microwave loss than the film surface.

Preparation of superconducting Tl-Ca-Ba-Cu thin films by chemical deposition

A chemical deposition process for the preparation of superconducting thin films of Tl2CaBa2Cu2O8 (2122) and Tl2Ca2Ba2Cu3O10 (2223) has been developed. Oriented, superconducting 2122 and 2223 thin films have been successfully fabricated on single-crystal yttria-stabilized zirconia and magnesium oxide substrates (〈100〉 orientation). Epitaxial films have been prepared on magnesium oxide. Chemical analysis of the film composition by energy dispersive x-ray analysis is in agreement (2122 vs 2223) with the phases indicated by powder x-ray diffraction. The thin films of these compounds exhibited superconducting transition temperatures above 105 K as determined by variable-temperature resistivity and ac magnetic susceptibility measurements. In addition, microwave surface resistance measurements at 150 GHz show that these films have very low losses at 77 K (1 mΩ).

Superconducting surface resistance of amorphous and crystalline Pb 55Bi 45

Measurements of microwave surface resistance can give information about electronic parameters in the amorphous and the crystalline state. The temperature dependence shows deviations from the BCS-function. Residual absorption in the superconducting state is less than 10 -3 of the normal state.