Point-Contact Spectroscopy in Mn-Doped MgB2 Single Crystals: Effects of Magnetic Impurities in a Two-Band Superconductor

We performed point-contact spectroscopy (PCS) measurements in Mg1−xMnxB2 single crystals, with x ≤ 0.015 and bulk Tc down to 13.3 K. The gaps σ and π were obtained by fitting the conductance curves of the point contacts with the two-band Blonder–Tinkham– Klapwijk (BTK) model. Both σ and π decrease with the critical temperature of the junctions TAc , but remain clearly distinct down to the lowest critical temperature (TAc∼=9 K). Once analyzed within the Eliashberg theory, the gap trends as a function of TAc can be explained by a doping-induced increase in the pair-breaking scattering within the σ band, with smaller contributions from the π-π or the σ-π channels.