Surface Superconductivity of Dirty Two-Band Superconductors: Applications to MgB₂

Original · EN

The minimal magnetic field Hc₂ destroying superconductivity in the bulk of a superconductor is smaller than the magnetic field Hc₃ needed to destroy surface superconductivity if the surface of the superconductor coincides with one of the crystallographic planes and is parallel to the external magnetic field. While for a dirty single-band superconductor the ratio of Hc₃ to Hc₂ is a universal temperature-independent constant 1.6946, for dirty two-band superconductors this is not the case. I show that in the latter case the interaction of the two bands leads to a novel scenario with the ratio Hc₃/Hc₂ varying with temperature and taking values larger and smaller than 1.6946. The results are applied to MgB₂ and are in agreement with recent experiments [A. Rydh et al., cond-mat/0307445].