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

TL;DR

This study investigates how magnetic Mn impurities affect the superconducting properties of MgB2 single crystals, revealing that spin-flip scattering dominates and impacts the two-band superconductivity.

Contribution

First directional point-contact measurements on Mn-doped MgB2, showing the effects of magnetic impurities on two-band superconductivity and spin-flip scattering.

Findings

Both gaps decrease with T_c^A but remain distinct.

Spin-flip scattering is dominant in the sigma band.

Results align with Eliashberg theory and band structure calculations.

Abstract

We present the first results of directional point-contact measurements in Mg_{1-x}Mn_{x}B_2 single crystals, with x up to 0.015 and bulk T_c down to 13.3 K. The order parameters Delta_{sigma} and Delta_{pi} were obtained by fitting the conductance curves with the two-band Blonder-Tinkham-Klapwijk (BTK) model. Both Delta_{pi} and Delta_{sigma} decrease with the critical temperature of the junctions T_c^A, 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 sigma band, as also confirmed by first-principle band structure calculations.