International Workshop on Electronic Crystals
S. Brazovskii, P. Monceau and N. Kirova
J. Phys. IV France 131 (2005) 15-19
DOI: 10.1051/jp4:2005131004

4K_F CDW induced by long range Coulomb interactions

F.Ya. Nad¹, P. Monceau², M. Nagasawa³ and T. Nakamura<sup>4

1</sup>  Institute of Radio-Engineering and Electronics, RAS, Moscow, Russia
²  Centre de Recherches sur les Très Basses Températures, Laboratoire associé à I'Université Joseph Fourier, BP. 166, 38042 Grenoble Cedex 9, France
³  Department Natural Science and Material Science, Tokyo Denki University, Japan
⁴  Institute for Molecular Science, Okazaki, Japan

Abstract
By method of dielectric spectroscopy we have obtained experimental data concerning the charge density wave (CDW) associated with the charge ordering (CO) state of Wigner type in (TMTTF)₂X conductors. A divergence of the relaxation time was found at the critical transition temperature into the CO state. Below a low frequency shoulder appears in the frequency dependence of the imaginary part of the dielectric permittivity. Under a moderate pressure, the peak in the real part of the dielectric permittivity, corresponding to the transition into the CO state, shifts to low temperature and broadens. The substitution of hydrogen by deuterium in TMTTF molecules results in an increase of (isotopic effect). The results obtained confirm the ferroelectric character of the CO state; they also favour long range Coulomb interactions as the main driven force for the formation of this state.

© EDP Sciences 2005