Peierls instabilities in quasi-one-dimensional quantum double-well chains

Abstract

Peierls-type instabilities in quarter-filled $(\mathrm{n\ifmmode \bar{}\else \={}\fi{}}=1/2)$ and half-filled $(\mathrm{n\ifmmode \bar{}\else \={}\fi{}}=1)$ quantum double-well hydrogen-bonded chain are investigated analytically in the framework of two-stage orientational-tunnelling model with additional inclusion of the interactions of protons with two different optical phonon branches. It is shown that when the energy of proton-phonon coupling becomes large, the system undergoes a transition to various types of insulator states. The influence of two different transport amplitudes on ground-state properties is studied. The results are compared with the pressure effect experimental investigations in superprotonic systems and hydrogen halides at low temperatures.