Vortex matter in the two-band superconductor MgB2

Abstract

The physics of vortex matter in MgB2, the first discovered technologically relevant ultiband superconductor (SC), are determined by the parameters of the two gaps and by their coupling. The interplay of the quasi-two-dimensional (2D) σ-band and the lmost isotropic π-band results in anomalous and complex behavior of the haracteristic lengths and critical fields. The coherence length and penetration depth are magnetic-field dependent, have different T dependence from those in single-band materials, and have different anisotropies. At low T and H the critical currents (Jc) are high and the relaxation rates (S) are low, indicative of large pinning energy. In clean MgB2, as H and T increases, the π-band contribution is strongly suppressed, so Jc decreases and S increases sharply, but C-doping allows maintaining strong pinning up to high fields as needed for applications.