Theoretical investigation of superconductivity in SrPd2Ge2, SrPd2As2, and CaPd2As2

Ab initio pseudopotential calculations have been performed to investigate the structural, electronic, and vibrational properties of SrPd2Ge2, SrPd2As2, and CaPd2As2 crystallizing in the ThCr2Si2-type body-centered tetragonal structure. Our electronic results show that the density of states at the Fermi level is mainly dominated by the strong hybridization of Pd d states and Ge (or As) p states. The linear response method and the Migdal-Eliashberg approach have been used to calculate the Eliashberg spectral function for all these compounds. By integrating the Eliashberg spectral function, the average electron-phonon coupling parameter (lambda) is found to be 0.74 for SrPd2Ge2, 0.66 for SrPd2As2, and 0.72 for CaPd2As2. Using the calculated values of lambda and the logarithmically averaged phonon frequency omega(ln) the superconducting critical temperature (T-c) values for SrPd2Ge2, SrPd2As2, and CaPd2As2 are found to be 3.20, 2.05, and 2.48 K, respectively, which are in acceptable agreement with the corresponding experimental values. The relative differences in the T-c values between the Ge and As compounds have been explained in terms of some key physical parameters.