This paper presents the frequency dependance of the proton spin-lattice relaxation time T1 at several temperatures and pressures in TTF-TCNQ(D4) and TTF(D4)-TCNQ. It is shown that only backward (q = 2 kF) and forward (q = 0) scatterings contribute to the nuclear relaxation induced by the modulation of the hyperfine field in these one-dimensional conductors. At medium fields, H 0 ~ 30 kOe, the frequency dependence of T1 originates from the diffuse character of the spin density wave excitations around q = 0, leading to T1-1 αH0- 1/2 . The enhancement of T1 -1, is at low fields, limited by the existence of a finite interchain coupling (tunnelling type). We find, within a RPA analysis, close correlations between the pressure and temperature dependences of the spin excitations diffusion constant and the collision time derived from the longitudinal conductivity. The interpretation of the NMR data in terms of a Hubbard model excludes both big U and small U pictures. However, we point out the importance of the electron-electron interactions on the relaxation rate of TTF-TCNQ. We derive a ratio U/4 t II ~ 0.9 for the TCNQ chain. We also assume that besides charge density waves fluctuations existing between 300 K and the phase transition at 53 K, electron-electron interactions make an important contribution to the temperature dependence of the spin susceptibility. Finally, we give a unified description of quasi one dimensional conductors in which the various systems are classified according to the transverse tunnelling coupling and the electron lifetime. It follows from this description that for TTF-TCNQ and its derivatives, transverse couplings (tunnelling and Coulomb) are large enough to justify the use of a mean-field theory

Dear Editors,We would like to submit our manuscript entitled "Dielectric response of charge induced correlated state in quasi-one-dimensional conductor (TMTTF) 2 PF 6 " for publication in Phys. Rev. We previously submitted it to Phys. Rev. Lett. (code number LH7335).The delay for resubmission has been caused by difficulties in communication between coauthors, one at Moscow, another visiting Japan during several weeks. We would like, however, the original received date to be retained. The manuscript has been amended according to the referee comments as described below :Referee A 1) We modified our description of the extended Mott-Hubbard model for half-filled bands (bottom of page 2) taking into account both the on-site interaction (U) and the near-neighbor interaction (V).2) The 2k F lattice fluctuations coupled to the lattice are observed at much lower temperature (below 60 K) than the large increase of the dielectric permittivity. We have rewritten the beginning of the discussion part, page 6, to make this point more clear. Referee B1) These organic conductors are very fragile and cracks may reflect significant strain when the cooling rate is too fast and/or the sample holding too tight. We used all the care possible for avoiding cracks in our crystals and thus measuring bulk properties.2) There is no evidence in (TMTTF) 2 PF 6 of a structural phase transition affecting the main Bragg reflections. The tentative explanation of our data is the occurrence of a superstructure (4k F ) transition. Such a transition could be very likely detected from NMR experiments.Yours sincerely, P. MONCEAU C e n t r e d e R e c h e r c h e s s u r l e s T rè s B a s s e s T e m pé r a t u r e s laboratoire associéà l'Université Joseph Fourier

Direct evidence of a new phase transition at TCO = 100.6 K in the organic quasi-one-dimensional (TMTTF)2AsF6 salt has been obtained from conductivity and dielectric permittivity measurements. This phase transition is assigned to a charge-ordered state (4kF charge density wave of Wigner type) due to charge-induced electron-electron interactions.