Recent first principles calculations of the phonon dispersion curves in MgB_2 have suggested the presence of anomalies in some of the curves, particularly in the longitudinal acoustical (LA) branch in the Gamma to A direction. Similar behavior has been observed in numerous other superconductors with T_c's higher than those of standard electron-phonon BCS superconductors. Phenomenological calculations of the Gamma->A LA dispersion based on both an acoustical plasmon and a ``resonant polarization'' mechanism are given here to emphasize the importance of these similarities.
@article{arxiv.cond-mat/0202050,
title = {Acoustic Phonon Anomaly in MgB2},
author = {R. F. Wood and Bo E. Sernelius and A. L. Chernyshev},
journal= {arXiv preprint arXiv:cond-mat/0202050},
year = {2009}
}