Abstract
We present the results of a crystal structure determination using neutron powder diffraction as well as the superconducting properties of the rare-earth sesquicarbide by means of specific-heat and upper critical field measurements. From the detailed analysis of the specific heat and a comparison with ab initio electronic structure calculations, a quantitative estimate of the electron-phonon coupling strength and the logarithmic average phonon frequency is made. The electron-phonon coupling constant is determined to be . The electron-phonon coupling to low energy phonon modes is found to be the leading mechanism for superconductivity. Our results suggest that is in the strong-coupling regime, and the relevant phonon modes are La related rather than C–C stretching modes. The upper critical field shows a clear enhancement with respect to the Werthamer-Helfand-Hohenberg prediction, consistent with the strong electron-phonon coupling. Possible effects on the superconducting properties due to the noncentrosymmetry of the crystal structure are discussed.
4 More- Received 22 February 2007
DOI:https://doi.org/10.1103/PhysRevB.76.014516
©2007 American Physical Society