Carbon substitution in MgB2 single crystals: Structural and superconducting properties

By S. Kazakov, R. Puźniak, K. Rogacki, A. Mironov, Nikolai Zhigadlo, J. Jun, C. Soltmann, B. Batlogg, J. Karpiński. 2004

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The growth of carbon-substituted magnesium diboride MgsB1˛xCxd2 single crystals with 0 x 0.15 is reported, and the structural, transport, and magnetization data are presented. The superconducting transition temperature decreases monotonically with increasing carbon content in the full investigated range of substitution. By adjusting the nominal composition, Tc of substituted crystals can be tuned in a wide temperature range between 10 and 39 K. Simultaneous introduction of disorder by carbon substitution and significant increase of the upper critical field Hc2 is observed. Comparing with the nonsubstituted compound, Hc2 at 15 K for x = 0.05 is enhanced by more than a factor of 2 for H oriented both perpendicular and parallel to the ab plane. This enhancement is accompanied by a reduction of the Hc2-anisotropy coefficient g from 4.5 sfor the nonsubstituted compoundd to 3.4 and 2.8 for the crystals with x = 0.05 and 0.095, respectively. At temperatures below 10 K, the single crystal with larger carbon content shows Hc2 sdefined at zero resistanced higher than 7 and 24 T for H oriented perpendicular and parallel to the ab plane, respectively. Observed increase of Hc2 cannot be explained by the change in the coherence length due to the disorder-induced decrease of the mean free path only.

Subfields: Condensed Matter Physics, Electronic, Optical and Magnetic Materials, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/19894ed2bf702254554bcd2b1722800184a4756f