On extrinsic effects in the surface impedance of cuprate superconductors by weak links

Journal Article · Wed Jan 01 04:00:00 EST 1992 · Journal of Applied Physics; (United States)

DOI:https://doi.org/10.1063/1.350711· OSTI ID:5526694

Halbritter, J ^[1]

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1. Kernforschungszentrum Karlsruhe, Institut fuer Materialforschung I, Postfach 36 40, 7500 Karlsruhe (Germany)

The reported rf surface impedance of superconducting cuprates continues to drop with 2 years of improving material quality. As leading indicator for quality the weak-link critical current {ital j}{sub {ital cJ}}({ital T}{approx} 0, {ital B} {approx} 0) has grown from 10{sup 2} to 10{sup 6} A/cm{sup 2} and thus the Josephson penetration depth {lambda}{sub {ital J}} {proportional to} 1/{radical}{ital j}{sub {ital cJ}} and the excess normal (leakage) tunnel current {ital j}{sub {ital bl}} are shrinking. This {ital j}{sub {ital cJ}} growth has now saturated, whereas the rf residual surface impedance {ital Z}{sub res} is still shrinking with material improvements. This shows clearly that {ital Z}{sub res} is an extrinsic property. Evidence that {ital Z}{sub res} is due to the large leakage current {ital j}{sub {ital bl}} and the small {ital j}{sub {ital cJ}} of weak links, where the latter destroys the intrinsic shielding from a {lambda}{sub {ital I}} thin-seam {lambda}{sub {ital J}} deep into the bulk, is presented. This causes rf residual losses {ital R}{sub res} {approx} ({omega}{mu}{sub 0}){sup 2}{lambda}{sub {ital J}}{sup 3}{sigma}{sub {ital bl}}/2. {ital R}{sub res} stays finite at {ital T} {congruent} 0 by {sigma}{sub {ital b}{ital l}}({ital T} {r arrow} 0) {approx} {sigma}{sub {ital bl}} ({proportional to}{ital j}{sub {ital bl}}) being amplified by ({lambda}{sub {ital J}}/{lambda}{sub {ital I}}){sup 3} {gt} 10{sup 3} as a weighting factor. With slow crystal growth weak links are improved and their density is reduced so that {ital R}{sub res} values better than {ital R}{sub Nb}(4.2 K) are now obtainable.

• OSTI ID: 5526694
• Journal Information: Journal of Applied Physics; (United States), Journal Name: Journal of Applied Physics; (United States) Vol. 71:1; ISSN 0021-8979; ISSN JAPIA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
AC LOSSES
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CRITICAL CURRENT
CURRENTS
ELECTRIC CURRENTS
ELECTRIC IMPEDANCE
ENERGY LOSSES
HIGH-TC SUPERCONDUCTORS
IMPEDANCE
JOSEPHSON EFFECT
LEAKAGE CURRENT
LOSSES
OXIDES
OXYGEN COMPOUNDS
PENETRATION DEPTH
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES