Interchain coupling and the Peierls transition in linear-chain systems

Abstract

We study the effect of interchain coupling on the Peierls transition temperature ${T}_{P}$ for a model with a nonplanar Fermi surface. Using the standard electron-phonon coupling, we show that the soft mode which causes the transition should have a wave vector ${q}_{0}=(\frac{\ensuremath{\pi}}{a}, \frac{\ensuremath{\pi}}{a}, 2{p}_{F})$. We evaluate the effect of interchain coupling on ${T}_{P}$ within the mean-field theory, as well as the effect of fluctuations. Both these effects reduce ${T}_{P}$, but we find that there is a range of interchain coupling where this reduction, due to both effects, is small. Neutron-scattering cross section and fluctuation contribution to the specific heat are evaluated. Comparison is made with experiments on ${\mathrm{K}}_{2}$Pt${(\mathrm{CN})}_{4}$${\mathrm{Br}}_{0.3}$\ifmmode\cdot\else\textperiodcentered\fi{}3${\mathrm{H}}_{2}$O (KCP) and tetrathiofulvalene-tetracyanoquinodimethan (TTF-TCNQ).