1. Generalized critical state model in high-Tc superconductors
- Author
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K. Yamafuji, T. Wakuda, and Takanobu Kiss
- Subjects
Physics ,Superconductivity ,Angular frequency ,Flux pinning ,High-temperature superconductivity ,Condensed matter physics ,General Physics and Astronomy ,law.invention ,symbols.namesake ,Maxwell's equations ,law ,Electric field ,symbols ,General Materials Science ,Critical current ,Current density - Abstract
It is shown theoretically that, in high- T c superconductors, the electric field E can be expressed approximately as a function of the current density J by E = \ g9 PF (J − J cm ) n at J ≥ J cm ∝ ( T g − T ) 2 ν ∝ ( B g − B ) 2 ν below the glass-liquid transition line given by T = T g ( B ) or B = B g ( T ). The above E versus J characteristic can be regarded as a generalization of the critical state model given by E = ϱ FF ( J − J c ) at J ≥ J c and also a modification of the n -value model given by E = \ g9J n . The applicability of the present model is confirmed by the fact that numerical solutions of the Maxwell equations with the proposed E versus J characteristic agreed quantitatively with the observed a.c. losses, including their dependences on the angular frequency ω. The analytic expressions for the a.c. loss under a d.c. bias field in a slab sample are shown to have the same forms as the well-known ones based on the Bean model for metallic superconductors, except for the fact that the critical current density J c should be replaced by J c e ff = J cm + δJ c ( ω ) with δJ c (ω) ∝ ω 1 n . The present expressions of the a.c. losses with the derived expressions for J c eff are shown to agree quantitatively with the observed data.
- Published
- 1997