Effect of magnetic field on the two superconducting gaps in MgB2 -: art. no. 132508

Double-gap superconductivity in an epitaxial MgB2 film has been studied by means of point-contact spectroscopy in magnetic field up to 8 T. The relatively fast disappearance of the feature associated with the pi-band gap at a field around 1 T is caused by the line broadening due to strong pair breaking rather than to a collapse of the double-gap state. This pair breaking was found to increase linearly with field. Field dependences of the order parameters Delta(pi) and Delta(sigma) in pi and sigma bands were measured in field applied parallel and perpendicular to the film, at T=4.2 K. In perpendicular field, both order parameters survive to a common H-c2, which is about 6.5 T for this direction. In parallel field, the decrease of the sigma gap is much more gradual, consistent with the H-c2 being about 4 times greater in this orientation. The difference in Delta(pi) measured in the two field orientations is however smaller than the difference of Delta(sigma). We compare these results with the data on tunnelling spectroscopy and specific heat measurements of MgB2 single crystals and find consistency between the different measurements.