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The Magnetic-field Dependence of the Gaps in a Two-band Superconductor: A Point-contact Study of MgB_2 Single Crystals

R. S. Gonnelli·D. Daghero·A. Calzolari·G. A. Ummarino·Valeria Dellarocca·V. A. Stepanov·J. Jun·S. M. Kazakov·J. Karpinski
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Abstract

We present the results of directional point-contact measurements in MgB_2 single crystals, in magnetic fields up to 9 T parallel to the c axis. By fitting the conductance curves of our point contacts -- showing clear Andreev-reflection features -- with a generalized Blonder-Tinkham-Klapwijk model, we were able to extract the values of the two gaps Delta_sigma and Delta_pi. The comparison of the resulting Delta_sigma(B) and Delta_pi(B) curves to the theoretical predictions of the two-band model in dirty limit, recently appeared in literature, allows the first direct test of this model and gives a clear and quantitative proof that the pi band, even in the best single crystals, is in the moderate dirty limit.

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R. S. Gonnelli, D. Daghero, A. Calzolari, G. A. Ummarino, Valeria Dellarocca, V. A. Stepanov, J. Jun, S. M. Kazakov, J. Karpinski. 2003-08-07. The Magnetic-field Dependence of the Gaps in a Two-band Superconductor: A Point-contact Study of MgB_2 Single Crystals. https://doi.org/10.1103/physrevb.69.100504

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