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; D. I. Khomskii

doi:10.1209/epl/i1996-00148-y

All issues

Volume 35 / No 7 (September I 1996)

Europhys. Lett., 35 7 (1996) 541-546

Abstract

Issue		Europhys. Lett. Volume 35, Number 7, September I 1996


Page(s)		541 - 546
Section		Condensed matter: electronic structure, electrical, magnetic and optical properties
DOI		https://doi.org/10.1209/epl/i1996-00148-y
Published online		01 September 2002

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. Knauf¹, J. Fischer¹, B. Roden¹, R. Borowski¹, B. Freitag¹, B. Büchner¹, H. Micklitz¹, A. Freimuth², V. Kataev³ and D. I. Khomskii⁴

¹ II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
² Physikalisches Institut, Universität Karlsruhe - 76128 Karlsruhe, Germany
³ Kazan Institute for Technical Physics, Russian Academy of Sciences, 420029 Kazan, Russian Federation
⁴ Material Research Center, Department of Physics, University of Groningen Nijenborgh 4, 9747 Ag Groningen, The Netherlands

Received: 17 June 1996
Accepted: 8 July 1996

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 $1\;\mu{\rm m}$ . In these small grains the Josephson contacts with negative critical current (π-junctions) generally involved to explain the WE must be able to carry a current density of order $j\approx 10^5\mbox{--}10^6\,{\rm A/cm}^2$ , even close to T_c. 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.

PACS: 74.25.Ha – Magnetic properties / 74.72.Hs – Bi-based compounds / 74.80.Bj – Granular, melt-textured, and amorphous superconductors; powders

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