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The superconducting gaps of C-substituted and Al-substituted MgB2 single crystals by point-contact spectroscopy
|Dario Daghero 1,4, Renato S. Gonnelli 1,4, Andrea Calzolari 1, Giovanni A. Ummarino 1,4, Valeria Dellarocca 1, Valeri A. Stepanov 3, Nikolai D. Zhigadlo 2, S. M. Kazakov 2, Janusz Karpinski 2|
1. INFM and Dipartimento di Fisica, Politecnico di Torino, Corso Duca degli Abruzzi, 29, Torino 10129, Italy
We report the results of the first directional point-contact measurements in Mg(B1-xCx)2 single crystals with 0 <= x <= 0.132 and in Mg1-yAlyB2 crystals with 0 <= y <= 0.21, obtained at ETH (Zurich) by means of a high-pressure technique in a cubic anvil. We made the point contacts by using the "soft" technique described elsewhere . The Andreev-reflection features of our conductance curves were measured in magnetic fields up to 9 T, applied either parallel to the c axis or to the ab plane of the crystals. By fitting the normalized conductance with the Blonder-Tinkham-Klapwijk (BTK) model generalized to the two-band case we obtained the dependence of the gaps Δπ and Δσ on the C or Al content (x or y). This dependence was confirmed by applying to the junctions a suitable magnetic field B* able to remove the contribution of the π-band gap to the total conductance, without appreciably affecting the σ-band one . This allowed the separate determination of the gaps via a single-band three-parameter BTK fit.
Presentation: oral at E-MRS Fall Meeting 2004, Symposium E, by Dario Daghero
See On-line Journal of E-MRS Fall Meeting 2004
Submitted: 2004-07-22 14:44 Revised: 2009-06-08 12:55