Carbon-substitution effect on the electronic properties of MgB2 single crystals -: art. no. 024504

The electronic properties of the carbon-substituted MgB2 single crystals are reported. The carbon substitution drops T-c below 2 K. In-plane resistivity shows a remarkable increase in residual resistivity by C substitution, while the change of in-plane/out-of-plane Hall coefficients is rather small. Raman scattering spectra indicate that the E-2g-phonon frequency radically hardens with increasing the carbon content, suggesting the weakening of electron-phonon coupling. Another striking C effect is the increases of the second critical fields in both in-plane and out-of-plane directions, accompanied by a reduction in the anisotropy ratio. The possible changes in the electronic state and the origin of T-c suppression by C substitution are discussed.