Theory of Structural Variation in a Quasi-One-Dimensional Conductor

Neutron-scattering studies of the quasi-one-dimensional conductor K₂Pt(CN)₄{Br}0.30·{H}₂$O demonstrate not only the existence of soft phonon modes but also the coexistence of central peaks and the development of a superlattice on cooling which, however, never becomes a true structural phase transition. We suggest that the central peak is due to bromine-induced, static, platinum-chain distortion and show that it affects the electronic motion sufficiently to create a strong enough fluctuation in the three-dimensional system to remove the expected phase transition.