The phonon-mode decomposition of the electron-phonon coupling in the MgB2-like system Li_{1-x}BC is explored using first principles calculations. It is found that the high temperature superconductivity of such systems results from extremely strong coupling to only ~2% of the phonon modes. Novel characteristics of E_2g branches include (1) ``mode lambda'' values of 25 and greater compared to a mean of ∼0.4 for other modes, (2) a precipitous Kohn anomaly, and (3) E_2g phonon linewidths within a factor of ~2 of the frequency itself, indicating impending breakdown of linear electron-phonon theory. This behavior in borne out by recent inelastic x-ray scattering studies of MgB2 by Shukla et al.
@article{arxiv.cond-mat/0207542,
title = {Extreme Electron-Phonon Coupling in Boron-based Layered Superconductors},
author = {J. M. An and S. Y. Savrasov and H. Rosner and W. E. Pickett},
journal= {arXiv preprint arXiv:cond-mat/0207542},
year = {2009}
}
Comments
4 two-column pages, 4 figures. Equations simplified. Figure 4 changed. Comparison with new data included