Crystal symmetry, electron-phonon coupling, and superconducting tendencies in Li2Pd3B and Li2Pt3B -: art. no. 174505

After theoretical determination of the internal structural coordinates in Li2Pd3B, we calculate and analyze its electronic structure and obtain the frequencies of the two A(g) phonons (40.6 meV for nearly pure Li mode, 13.0 meV for the strongly mixed Pd-Li mode). Pd can be ascribed a 4d(10) configuration, but strong 4d character remains up to the Fermi level. Small regions of flat bands occur at -70 meV at both the Gamma and X points. Comparison of the Fermi level density of states to the linear specific heat coefficient gives a dynamic mass enhancement of lambda=0.75. Rough Fermi surface averages of the deformation potentials D of individual Pd and Li displacements are obtained. While < D-Li > is small, < D-Pd >approximate to 1.15 eV/A is sizable, and a plausible case exists for its superconductivity at 8 K being driven primarily by coupling to Pd vibrations. The larger d bandwidth in Li2Pt3B leads to important differences in the bands near the Fermi surface. The effect on the band structure of spin-orbit coupling plus lack of inversion is striking, and is much larger in the Pt compound.