A comparative ab initio study of superconductivity in the body centered tetragonal YC2 and LaC2

Abstract

Ab initio studies of the electronic band structure and phonon dispersion relations, using the planewave pseudopotential method and the density functional theory, have been made for the superconducting materials YC2 and LaC2. Differences in the phonon spectrum and density of states both in the acoustical and optical ranges between these materials are investigated and discussed. By integrating the Eliashberg spectral function alpha F-2(omega), the average electron-phonon coupling parameter is found to be lambda = 0.55 for YC2 and 0.54 for LaC2, indicating these to be weak-coupling BCS superconductors. It is established that about 60% of lambda is contributed by acoustic phonons in both materials. Using a reasonable value of mu* = 0.13 for the effective Coulomb repulsion parameter, the superconducting critical temperature T-c is found to be 3.81K for YC2 and 2.44K for LaC2, in good agreement with values reported from experimental measurements. (C) 2015 AIP Publishing LLC.