Gap formation and soft phonon mode in the Holstein model.

  title={Gap formation and soft phonon mode in the Holstein model.},
  author={Donovan Meyer and Alex C. Hewson and Ralf Bulla},
  journal={Physical review letters},
  volume={89 19},
We investigate electron-phonon coupling in many-electron systems using the dynamical mean-field theory in combination with the numerical renormalization group. This nonperturbative 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.