A Point-Contact Study of the Superconducting Gaps in Al-Substituted and C-Substituted MgB₂ Single Crystals
Gonnelli, R. S. · Daghero, D. · Ummarino, G. A. · Calzolari, A. · Dellarocca, Valeria · Stepanov, V. A. · Kazakov, S. M. · Jun, J. · Karpinski, J.
Original · EN
We present the results of directional point-contact spectroscopy in state-of-the-art Mg₁₋ₓAlₓB₂ and Mg(B₁₋yCy)₂ single crystals produced at ETH, Zurich. Fitting the conductance curves of our point contacts, that always feature Andreev reflection structures, we obtained the doping dependence of the gap amplitudes. The results are discussed in comparison with other experimental findings and relevant theoretical predictions. We conclude that the physics of Al-substituted crystals at x > 0.09 might be governed by phase segregation, while C-substituted crystals unexpectedly show a doping-induced transition to single-gap superconductivity at y=0.132.
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