We investigate electron-phonon coupling in many-electron systems using dynamical mean-field theory in combination with the numerical renormalization group. This non-perturbative method reveals significant precursor effects to the gap formation at intermediate coupling strengths. The emergence of a soft phonon mode and very strong lattice fluctuations can be understood in terms of Kondo-like physics due to the development of a double-well structure in the effective potential for the ions.
@article{arxiv.cond-mat/0206366,
title = {Gap formation and soft phonon mode in the Holstein model},
author = {D. Meyer and A. C. Hewson and R. Bulla},
journal= {arXiv preprint arXiv:cond-mat/0206366},
year = {2009}
}