Search

We present a brief review of results on the surface impedance of cuprate superconductors, focusing mainly on YBa2Cu3O7-(delta ) (YBCO) and evidence of d-wave superconductivity in that material. We then discuss our recent results on Ba-K-Bi-O thin films, and the effects of DC electric fields on the surface impedance of YBCO films. A summary of our data on high quality thin films and single crystals of the electron-doped Nd1.85Ce0.15CuO4-(delta ) (NCCO) cuprate superconductor follows. Surprisingly, the measurements on NCCO are consistent with the behavior of an s-wave BCS superconductor, in striking contrast to recent results on YBCO. Finally we discuss some of the interesting potential implications of d-wave superconductivity for microwave applications of the cuprates.

A high-Ta field-effect transistor-like structure (SuFET) was made which consisted of an ultrathinYBa2Cu3O (YBCO) film, a dielectric SrTiO3 layer and a gold gate electrode. The use of ultrathin filmsof a few unit cells thickness and an epitaxially grown dielectric layer allowed a relative change in the arealcarrier density of YBCO in excess of 20%. A comparable amount of modulation was obtained in normal

Recent accomplishments such as the demonstration of low microwave surface resistance over a wide range of frequencies and low magnetic flux noise in high quality thin films of the 90 K superconductor YBa2Cu3O7-x (YBCO), have heightened the hope that the new high temperature superconductors (HTSC) can play an important technological role. With improvement in the quality of films, very exciting superconducting state properties which till now were masked by inhomogeneities introduced by the fabrication processes, are beginning to be uncovered. Progress in these areas has been easiest for those in the community who initially chose to focus on understanding the materials issues relating to the growth of high quality thin films and single crystals. Current techniques for studying these materials include measurements of the high frequency response of single layer YBCO films in order to reveal the intrinsic properties of the superconductors and gauge their suitability for technological applications. By alloying the superconductors in the cation sites, we can also extract information on the mechanisms of superconductivity in these systems, generate new families of lattice matched materials, such as the Y1-yPryBa2Cu3O7-x system which for y=0 to 1 possess a variety of electrical properties and can form building blocks for multilayer junctions or superlattices.