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 Mg_1−x Mn _x B₂ single crystals, with x≤0.015 and bulk T _c down to 13.3 K. The gaps Δ _σ and Δ _π were obtained by fitting the conductance curves of the point contacts with the two-band Blonder–Tinkham–Klapwijk (BTK) model. Both Δ _σ and Δ _π decrease with the critical temperature of the junctions T _c ^A , but remain clearly distinct down to the lowest critical temperature (T _c ^A ≅9 K). Once analyzed within the Eliashberg theory, the gap trends as a function of T _c ^A 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.