PERIOD-DOUBLING IN QUASI-ONE-DIMENSIONAL SYSTEMS - A NONADIABATIC APPROACH

In this article we propose a new approach to the electron-phonon probl em in partially filled bands. With the help of the 'rotating wave appr oximation' we derive a reduced hamiltonian that can partially be diago nalized analytically in a many-particle basis. Structurally different many-particle states show up. While in the conventional adiabatic trea tment Of quasi-one-dimensional systems already an arbitrary small elec tron-phonon coupling can lead to a Peierls-type distortion, within the here proposed formalism we may conclude that a critical coupling stre ngth has to be overcome for an energy gap above the highest occupied s tate to occur.