Theoretical investigation of superconductivity inSrPd2Ge2,SrPd2As2, andCaPd2As2

Abstract

Ab initio pseudopotential calculations have been performed to investigate the structural, electronic, and vibrational properties of ${\mathrm{SrPd}}_{2}{\mathrm{Ge}}_{2}, {\mathrm{SrPd}}_{2}{\mathrm{As}}_{2}$, and ${\mathrm{CaPd}}_{2}{\mathrm{As}}_{2}$ crystallizing in the ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-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 $(\ensuremath{\lambda})$ is found to be 0.74 for ${\mathrm{SrPd}}_{2}{\mathrm{Ge}}_{2}$, 0.66 for ${\mathrm{SrPd}}_{2}{\mathrm{As}}_{2}$, and 0.72 for ${\mathrm{CaPd}}_{2}{\mathrm{As}}_{2}$. Using the calculated values of $\ensuremath{\lambda}$ and the logarithmically averaged phonon frequency ${\ensuremath{\omega}}_{ln}$ the superconducting critical temperature $({T}_{c})$ values for ${\mathrm{SrPd}}_{2}{\mathrm{Ge}}_{2}, {\mathrm{SrPd}}_{2}{\mathrm{As}}_{2}$, and ${\mathrm{CaPd}}_{2}{\mathrm{As}}_{2}$ 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.