Europhys. Lett, 35 (7), pp. 541-546 (1996)
Wohlleben effect in small grains of Bi-based high-temperature superconductors: evidence for intrinsic nature of spontaneous currents
N. Knauf , J. Fischer , B. Roden , R. Borowski , B. Freitag , B. Büchner , H. Micklitz , A. Freimuth , V. Kataev and D. I. Khomskii
II. Physikalisches Institut,
Universität zu Köln,
Zülpicher Str. 77, 50937 Köln, Germany
Physikalisches Institut, Universität Karlsruhe - 76128 Karlsruhe, Germany
Kazan Institute for Technical Physics, Russian Academy of Sciences, 420029 Kazan, Russian Federation
Material Research Center, Department of Physics, University of Groningen
Nijenborgh 4, 9747 Ag Groningen, The Netherlands
(received 17 June 1996; accepted in final form 8 July 1996)
PACS. 74.25Ha - Magnetic properties.
PACS. 74.72Hs - Bi-based compounds.
PACS. 74.80Bj - Granular, melt-textured, and amorphous superconductors; powders.
Abstract:We report on the observation of the Wohlleben effect (WE) in powders of Bi-based high-temperature superconductors consisting of isolated grains with sizes of order . In these small grains the Josephson contacts with negative critical current (-junctions) generally involved to explain the WE must be able to carry a current density of order , even close to . Such high spontaneous currents can be explained, if such contacts are not ordinary tunneling Josephson junctions but superconductor--normal-metal--superconductor junctions and if the superconducting order parameter has d-wave symmetry.
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