Abstract
The growth of carbon-substituted magnesium diboride single crystals with 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, 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 is observed. Comparing with the nonsubstituted compound, at 15 K for is enhanced by more than a factor of 2 for oriented both perpendicular and parallel to the plane. This enhancement is accompanied by a reduction of the -anisotropy coefficient from 4.5 (for the nonsubstituted compound) to 3.4 and 2.8 for the crystals with and 0.095, respectively. At temperatures below 10 K, the single crystal with larger carbon content shows (defined at zero resistance) higher than 7 and 24 T for oriented perpendicular and parallel to the plane, respectively. Observed increase of cannot be explained by the change in the coherence length due to the disorder-induced decrease of the mean free path only.
2 More- Received 30 April 2004
DOI:https://doi.org/10.1103/PhysRevB.71.024533
©2005 American Physical Society