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

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Some DC Hall effect measurements have been made on single crystals of TTF-TCNQ in the metallic region, at atmospheric pressure and under pressure of 6 kbars. For the field orientation employed here (H parallel to the crystalline a axis) the average value of the low field Hall coefficient is — 4.2 ± 0.6 x 10-11 Vcm/AG at room temperature which is approximately consistent with other estimates of the electron density. The influence of the electrical contacts is discussed in detail and the temperature dependence of RH is compared with previous work on HMTSF-TCNQ

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Nous présentons des mesures de compressibilité de TTF-TCNQ deutéré par diffraction de neutrons sous hautes pressions hydrostatiques jusqu'à ~ 20 kbar à la température ambiante. Les valeurs observées sont respectivement suivant les axes a, b et c, ka = 2,7, kb = 4,7 et kc = 3,2 x 10-12 cm2/dyne. Ces résultats indiquent l'existence d'une contribution importante de type électrostatique (coulomb) à l'interaction interchaînes. Nous suggérons que la cohésion des cristaux de TTF-TCNQ provient de l'empilement de dipôles moléculaires fluctuants. Abstract.-The linear axial compressibilities of a deuterated sample of TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane) have been measured by a neutron diffraction technique under hydrostatic pressures up to ~ 20 kbar at room temperature. The observed compressibilities along the crystallographic axes are, respectively, ka = 2.7, kb = 4.7 and kc = 3.2 x 10-12 cm2/dyne. These results indicate a strong Coulomb type interchain interaction. It is suggested that the dominant part of the crystal cohesion results from a stacking of strongly dynamically polarized TTF and TCNQ molecules acting as effective molecular dipoles.