Effect of magnetic impurities in a two-band superconductor: A point-contact study of Mn-substituted MgB2 single crystals

We present the first results of directional point-contact measurements in Mg1xMnxB2 single crystals, with x up to 0.015 and bulk Tc down to 13.3 K. The order parameters and were obtained by fitting the conductance curves with the two-band Blonder-Tinkham-Klapwijk model. Both and decrease with the critical temperature of the junctions TAc , but remain clearly distinct up to the highest Mn content. Once analyzed within the Eliashberg theory, the results indicate that spin-flip scattering is dominant in the band, as also confirmed by first-principles band-structure calculations.