Ab initio investigation of BCS-type superconductivity in LuNi2 B2 C -type superconductors

Abstract

Ab initio pseudopotential calculations have been made to calculate the structural, electronic, vibrational, and superconducting properties of the borocarbide superconductors RM2B2C(R=Lu,La,Y;M=Ni,Pd,Pt). Using the electronic and vibrational spectra, the average electron-phonon coupling parameter is calculated to be 0.78, 0.83, 0.96, and 1.48 for LaPt2B2C, LuNi2B2C, YPt2B2C, and YPd2B2C, respectively. From a detailed spectral analysis throughout the irreducible Brillouin zone (IBZ), we found that the highest contribution to the electron-phonon coupling parameter for these materials comes from the acoustic and low-frequency optical modes characterized with anomalous dispersion, instead of the A1g optical-phonon mode claimed in previous studies. Using the calculated electron-phonon coupling parameter values, the superconducting critical temperatures for LaPt2B2C, LuNi2B2C, YPt2B2C, and YPd2B2C are found to be 10.40, 15.94, 11.30, and 20.60 K, respectively, which are in good accordance with their experimental values of 10.50, 16.10, 10.00, and 21.00 K.