Identification of specific phonon contributions in BCS-type superconductivity of boride-carbide crystals with a layer-like structure

• The electronic structures of YPd2B2C, YPt2B2C and LaPt2B2C are studied using ab initio pseudopotential method.
• Phonons are studied using a linear response theory.
• The lowest phonon mode couples more strongly with electrons.
• The calculated TC of 20.6 K for YPd2B2C is in agreement with the experimental value of 21 K.

We report on an ab initio study of the BCS-type superconductivity in the intermetallic borocarbides YPd2B2C, YPt2B2C and LaPt2B2C with a layer-like structure. The largest contribution to the electron-phonon coupling constant λ is identified to come from transverse acoustic phonons at a zone-edge, arising from the atomic vibrations in the boron-transition metal layer. A detailed examination of the atomic geometry in the boron-transition metal layer, the electron-phonon coupling constant λ  , and the logarithmically averaged phonon frequency ωlnωln helps explain the relatively higher superconducting temperature Tc of YPd2B2C (20.6 K) compared to that of YPt2B2C (11.3 K) and LaPt2B2C (10.40 K).