Phonon dispersion and electron-phonon coupling in MgB_2 and AlB_2

Details Phonon dispersion and electron-phonon coupling in MgB_2 and AlB_2 Phonon dispersion and electron-phonon coupling in MgB_2 and AlB_2

2001-03-15

arxiv.org/abs/cond-mat/0103319v2

Physics

Condensed Matter

Superconductivity

10 pages, 4 figures, to appear in Phys. Rev. Lett

Scientific paper

10.1103/PhysRevLett.86.5771

We present a first principles investigation of the lattice dynamics and electron-phonon coupling of the superconductor MgB_2 and the isostructural AlB_2 within the framework of density functional perturbation theory using a mixed-basis pseudopotential method. Complete phonon dispersion curves and Eliashberg functions \alpha^2F are calculated for both systems. We also report on Raman measurements, which support the theoretical findings. The calculated generalized density-of-states for MgB_2 is in excellent agreement with recent neutron-scattering experiments. The main differences in the calculated phonon spectra and \alpha^2F are related to high frequency in-plane boron vibrations. As compared to AlB_2, they are strongly softened in MgB_2 and exhibit an exceptionally strong coupling to electronic states at the Fermi energy. The total coupling constants are \lambda_{MgB_2}=0.73 and \lambda_{AlB_2}=0.43. Implications for the superconducting transition temperature are briefly discussed.

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