It was noted that the minimum magnetic field, HC2, which destroyed superconductivity in the bulk of a superconductor was smaller than the magnetic field, HC3, needed to destroy surface superconductivity, if the surface of a superconductor coincided with one of the crystallographic planes and was parallel to the external magnetic field. While for a dirty single-band superconductor the ratio, HC3/HC2, was a universal temperature-independent constant, 1.6946, this was not the case for dirty 2-band superconductors. It was shown that, in the latter case, the interaction of the 2 bands led to a novel scenario; with the HC3/HC2 ratio varying with temperature and taking values both larger and smaller than 1.6946.

Surface Superconductivity of Dirty Two-Band Superconductors - Applications to MgB2. D.A.Gorokhov: Physical Review Letters, 2005, 94[7], 077004 (3pp)