E. B. Klyuenkov

Structure of the mixed state induced in thin YBaCuO superconducting films by the field of a small ferromagnetic particle

The temperature dependence of the local energy barrier to formation of the mixed state in YBaCuO thin-film superconducting samples has been determined. The measurement technique is based on use of a small ferromagnetic particle as the magnetic field source. It is found that the energy barrier to creation of vortices (for the field oriented parallel to the CuO planes) is anomalously small while the dependence of the corresponding threshold current jc(T) differs substantially from the temperature dependence of the pair-breaking current. The experimental results are interpreted in terms of the model of a Josephson medium. The observed temperature dependence of jc points to a strong suppression of the superconducting order parameter at the intergrain boundaries, which for the most probable type of boundaries: superconductor-insulator-superconductor, is evidence of anisotropic pairing.

Special features in the synthesis and properties of thin Y-Ba-Cu-O high-temperature superconductor films free of secondary phases

Data on the structure and transport properties of thin Y-Ba-Cu-O (YBCO) high-temperature superconductor films obtained by magnetron sputtering of a stoichiometric target in a system with a 90° off-axis geometry are reported. It is shown that the films prepared under these conditions are free of copper-rich secondary phases and are characterized by the surface roughness height below 10 nm. The films possess a perfect structure and exhibit high superconducting properties: c-axis misorientation in microblocks FWHM(005)YBCO=0.4–0.5°; zero-resistance temperature Tco=89 K; critical (pinning) current density jp=1.5–2 MA/cm2 (77 K).

Investigation of inhomogeneities in thin films of high-temperature superconductors by scanning probe microscopy

Scanning tunneling microscopy and atomic force microscopy were used to study inhomogeneities in thin films of Y-Ba-Cu-O high-temperature superconductors caused by secondary-phase precipitates. It was established that Y-Ba-Cu-O films with high global critical parameters may constitute a complex heterogeneous system containing regions of different thickness and electrical properties. It is shown that these inhomogeneities may strongly influence the parameters of devices formed using these films.

Influence of working gas pressure on the properties of thin films of high-temperature superconductors obtained by magnetron sputtering

The surface morphology, composition, microstructure, and electrical properties of thin films of YBa2Cu3O7−x high-temperature superconductors, obtained by inverted magnetron sputtering, have been studied as a function of the pressure of the working gas mixture and results are presented. The main parameters of the magnetron discharge plasma near the substrate were determined by analyzing the characteristics of Langmuir probes. Changes in the properties of the films are considered to be caused by bombardment of the growing film with plasma ions accelerated in the floating potential field of the substrate. Films obtained at a pressure of 28 Pa and substrate temperature of 630 °C had a superconducting transition end temperature Tc,off=89 K and a critical current density jc=2 MA/cm2 (at 77 K) and were free from secondary phase particles larger than 10 nm.

Influence of desorption on the composition of high-temperature superconducting thin films during magnetron sputtering

Results are presented of investigations to study how desorption caused by interaction between the surface of condensation and the plasma particles affects the composition of thin films of Y-Ba-Cu-O high-temperature superconductors during magnetron sputtering. An analysis of the current-voltage characteristics of Langmuir probes was used to determine the floating potential of the substrate at various working gas pressures. Electron Auger spectroscopy was used to determine the atomic composition of films obtained at various substrate bias voltages. It was established that during magnetron sputtering of Y-Ba-Cu-O films the formation of the condensate composition may be strongly influenced by selective desorption of components from the substrate and the surrounding structural elements as a result of bombardment by plasma ions accelerated in the floating potential field.