Stochastic models for the depolarization of immobile spins by single diffusing impurities

The structure of one-dimensional systems with a half-filled band is discussed. In addition to lattice coordinates several intramonomer coordinates are considered. It is found that the system distorts and dimerizes (Peierls distortion). The distortions can be caused by lattice coordinates, by intramonomer coordinates or by both types of coordinates simultaneously. Thereby the various intramonomer degrees of freedom act cooperatively. The interplay between the intramonomer and lattice coordinates may induce new types of phase transitions with critical temperatures below the usual Peierls transition. Depending on the values of the effective matrix elements up to two of these new transitions may occur for a given system. The impact of these additional phase transitions on the specific heat, energy gap and lattice structure is discussed.