Three-dimensional ordering in HMTTF-TCNQ

2014 We examine the Ginzburg-Landau model for the Peierls instability in HMTTFTCNQ and show that the three-dimensional ordering is dominated by the diagonal coupling between TCNQ chains in the alternating chain lattice. The transverse wave vector can be incommensurate and nearly constant in the wide temperature range below a common critical temperature (50 K) for both families of chains. We find that just below this temperature the ordering is dominated by the TCNQ chains, while the deformation of the HMTTF chains remains weak until about 43 K and then sharply increases. Thus we expect one phase transition temperature but two anomalies in physical properties. These results are consistent with the experimental observations of diffuse X-ray scattering, transport properties and specific heat. LE JOURNAL DE PHYSIQUE LETTRES TOME 39, 1 er OCTOBRE 1978,