Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 26: Superconductivity: Vortex Dynamics, Vortex Phases, Pinning
TT 26.1: Vortrag
Mittwoch, 27. Februar 2008, 15:45–16:00, H 3010
General critical state in type-II superconductors with longitudinal currents — •Ernst Helmut Brandt1 and Grigorii Mikitik1,2 — 1Max-Planck-Institut für Metallforschung, Stuttgart — 2B. Verkin Institute for Low Temperature Physics and Engineering, NUAS, Kharkov, Ukraine
The concept of the Bean critical state has been very successful in superconductors with vortex pinning. It states that the current density |j| is either zero or jc, the critical current density, and it thus predicts sharp spatial jumps of j. However, this usual critical state model applies only when j is perpendicular to the vortex lines everywhere. We generalize this model to the frequent situation when j(r) is at arbitrary angle with respect to the induction B(r), by postulating that only the perpendicular component j⊥ (which causes the Lorentz force) is critical, j⊥≤ jc. Surprisingly, even for the simple example of a slab in rotating magnetic field such that no flux cutting occurs, the resulting spatial profiles of j(x) and B(x) in the critical state are now smooth, diffusion like, and do not exhibit the expected sharp fronts.
[1] E. H. Brandt and G. P. Mikitik, Phys. Rev. B 76, 64526 (2007).