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Förderbeginn 01.01.2001

Limitierungen in der Anwendung von Hochtemperatur-Supraleitern (HTSL) als kompakte, niederenergetische Mikrowellen-Vorrichtungen

Prof. Dr. Werner Hanke
Universität Würzburg
Lehrstuhl für Theoretische Physik I

Prof. Dr. Doug J. Scalapino
University of California, Santa Barbara
Department of Physics


Dünne Filme von Hoch-Tc-Supraleitern können sich als kompakte Mikrowellen-Resonatoren, Filter etc. eignen. Der niedrige Oberfächenwiderstand dieser Materialen bei Temperaturen des flüssigen Stickstoffs erlaubt die Konstruktion kompakter, sehr effizienter Vorrichtungen, die bei gleichzeitiger größerer Leistung kleinere Abmessungen aufweisen. In dem Projekt soll in einer engen Zusammenarbeit des Lehrstuhls für Theoretische Physik I (Prof. Hanke), Univer-sität Würzburg, mit Prof. D. J. Scalapino (University of California, Santa Barbara) geklärt werden, welche Verbesserung man konkret im Fall der HTSL-Filter etc. erwarten kann.

Abschlussbericht
Thin film high-Tc superconducting circuits offer the promise of providing compact microwave resonators, filters and delay lines. The low surface resistance of these materials at liquid nitrogen temperatures, i.e. around the superconducting transition temperatures, allows the design of compact, “high quality” circuits, increasing the performance and reducing the size, compared to conventional devices.

In the co-operation between Prof. Dr. D. J. Scalapino, University of California, Santa Barbara and the German contact person Prof. Dr. W. Hanke, Institute for Theoretical Physics and Astrophysics, University of Würzburg the intrinsic limiting behavior that one might achieve with a perfect film and what the limiting behaviour implies for HTSC filters, have been explored and studied.

In order to replace the presently more or less entirely empirical search for significantly improved low-power rf –filters etc., by a systematic scheme, the physics of the HTSC at and around superconducting transition temperatures has been studied.

In particular, we have investigated the influence of the so-called pair-phase fluctuations on the electronic and superconducting properties of the Copper oxide high-temperature materials. These phase fluctuations play no role in the conventional low temperature superconductors, but acquire a dominant influence on the electronic and optical properties between the superconducting transition temperature Tc (typically 100° Kelvin) and a much higher temperature, called mean-field transition temperature (around several hundred degree Kelvin). This regime is called pseudo gap regime, since it exhibits a superconducting-like gap in the electronic excitations even above Tc. This pseudo gap behavior determines crucially the intrinsic limits, which one might achieve with a perfect film and also the limiting behavior of the HTS filters.

I would like to use the opportunity to thank the Bavaria California Technology Center for their generous travel support.