WOLTE 2
Proceedings of the Second European Workshop on Low Temperature Electronics

J. Phys. IV France 06 (1996) C3-329-C3-334
DOI: 10.1051/jp4:1996350

Basic Aspects of High-T_c Grain Boundary Devices

J. Mannhart¹, H. Hilgenkamp¹, B. Mayer¹, Ch. Gerber¹, J.R. Kirtley², K.A. Moler^{2, 3} and M. Sigrist<sup>4

1</sup>  IBM Research Division, Zurich Research Laboratory, 8803 Rüschlikon, Switzerland
²  IBM Research Division, T.J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598, U.S.A.
³  Present address : Dept. of Physics, Princeton University, Princeton, NJ 08536, U.S.A.
⁴  Theoretische Physik, ETH-Hönggerberg, 8093 Zürich, Switzerland

Abstract
Grain boundaries are extensively used as high-quality Josephson junctions in high-T_c superconductors. Their superconducting characteristics can generally be well described by conventional models of strongly coupled Josephson junctions. Here, we report on highly anomalous critical current vs. magnetic field dependencies of grain boundaries in YB_a2Cu₃O_7-x. Direct imaging with scanning SQUID microscopy provides evidence of magnetic flux generated by single grain boundaries. Conventional Josephson junction models cannot explain these effects if a superconducting order parameter with a pure s-wave symmetry is assumed. The results have significant implications for our understanding of the properties of grain boundaries in high-T_c superconductors and for their applications.

© EDP Sciences 1996