Dresden 2003 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 5: Supraleitung: Massivmaterialien, Bandleiter, Pinning, Vortexdynamik, Transporteigenschaften, Korngrenzen I
TT 5.5: Vortrag
Montag, 24. März 2003, 15:45–16:00, HSZ304
PERCOLATION and PINNING in SUPERCONDUCTING MgB2 in RELATION to Nb-, NbN,- and HTS-SUPERCONDUCTORS — •Juergen Halbritter — Forschungszentrum Karlsruhe, Institut fuer Materialforschung I, Postfach 3640, 76021 Karlsruhe, Germany
The hindrance of electric transport by grain/island boundaries in distances aJ( ≤ 1µm) is well accepted in the normal conducting state, whereas related critical Josephson current densities jcJ are less well known. For a quantitative model the resistivity [1]
| ρ(T) = Rbn/aJ + p(ρ i(T) + ρ i(0)) (1) |
is fitted to observations yielding boundary resistances
Rbn(Ωcm2), residual resistances by scattering in
the grains ρ i(0) and percolation factors p>1 by current
diverting boundaries with Rbn ≥ mΩcm2. Like in
the case of HTS where for critical current densities
jc(H<Hc1)≃ jcJ(H) holds by Josephson fluxon
pinning with jcJRbn2≃ 10−12 VΩcm2 in
MgB2 jcJRbn≃ Δ/e fit the data. Relevant
tunnel and scattering processes will be discussed.
1 J. Halbritter, Phys. Rev. B 48, 9735
(1993) and Supercond. Sci. Technol. 12, 883 (1999).