[Zurück]

M. Eisterer, C. Krutzler, M. Zehetmayer, H. W. Weber, S. Kazakov, J. Karpinski:
"Two-band character of MgB₂ - magnetization of MgB₂ single crystals";
Vortrag: CIMTEC 2006, Acireale (Italien) (eingeladen); 04.06.2006 - 09.06.2006.

The reversible magnetization of MgB2 singe crystals is strongly influenced by the two-band character of this superconductor. At low magnetic fields charge carriers of both bands contribute nearly equally to superconductivity and to the related diamagnetism. With increasing field the order parameter in the pi-band decreases faster than in the sigma-band, due its smaller "intrinsic" upper critical field. At high magnetic fields charge carriers of the pi-band remain superconducting only due to their interaction with the sigma-band. Because of these changing contributions of the bands, the magnetization cannot be described by the usual Ginzburg-Landau (GL) theory. An extension of this theory to two band superconductors is required, where the magnetic penetration depth and the "effective" coherence length become field dependent. The model is compared to experiments on pure and carbon doped single crystals and allows to extract the magnetic penetration depth. Carbon doping significantly increases the magnetic penetration depth, but reduces its field dependence.