Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 1: Supraleitung: Herstellung und Charakterisierung
TT 1.5: Vortrag
Montag, 8. März 2004, 10:30–10:45, H20
Mechanisms of current improvement at grain boundaries in High-Tc superconductors: Magneto-optic and electron-optic results — •Christian Jooss1, Karsten Guth1, Volker Born1, Eva Brinkmeier1, Harald Jarzina1, Wilko Westhäuser1, Marvin Schofield2, Marco Beleggia2, and Yimei Zhu2 — 1Institut für Materialphysik, Universität Göttingen, Tammannstr. 1, 37077 Göttingen — 2Brookhaven National Laboratory, Upton, NY 11973 USA
Grain boundaries in high-temperature superconductors represent the major factor limiting high current applications. We apply a full quantitative magneto-optical imaging technique to the investigation of local transport properties of low angle grain boundaries in YBaCuO and Ca-doped YBaCuO thin films. In order to analyse microscopic mechanisms of current suppression, the local transport measurements grain boundaries are combined with the determination of electrostatic potentials by electron holography. By developing quantitative phase retrieval procedures for electron holography, we obtained for the first time direct evidence of a negative potential at the grain boundary dislocations which is significantly reduced in its spatial extend as well as in its value in Ca-doped samples. Our results nicely explain the observed enhancement of the intergranular current densities by Ca-doping and shed light onto the puzzling electronic properties of high-temperature superconducting oxides at grain boundaries. We find evidence for the presence of a new insulating electronic phase at the grain boundary in the strongly overdoped region. This work is partially supported by the Deutsche Forschungsgemeinschaft (DFG).