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An investigation of the P/T phase diagram of the quarter-filled organic conductors, [EDT-TTF-CONMe 2 ] 2 X is reported on the basis of transport and NMR studies of two members, X=AsF 6 and Br of the family. The strongly insulating character of these materials in the low pressure regime has been attributed to a remarkably stable charge ordered state confirmed by 13 C NMR and the only existence of 1/4 Umklapp e-e scattering favoring a charge ordering instead of the 1D Mott localization seen in (TM) 2 X which are quarter-filled compounds with dimerization. A non magnetic insulating phase instead of the spin density wave state is stabilized in the deconfined regime of the phase diagram. This sequence of phases observed under pressure may be considered as a generic behavior for 1/4-filled conductors with correlations. 1Superconductivity is just one of many phases exhibited by the (TM) 2 X series of organic salts (where TM stands for TMTTF or TMTSF donor molecules) and for which correlations play a central role. This is illustrated by their phase diagram studied under pressure or magnetic field [1,2]. The fact that most members of the (TMTTF) 2 X series behave as insulators under ambient pressure is of interest since on the basis of chemistry, structure and stoichiometry, conducting behavior is expected from the existence of partially filled bands.The insulating ground states originate with electronic correlations, which take on an enhanced importance in the case of the quasi-one dimensional nature of the transfer integrals that applies here: (t a : t b : t c =200meV:12meV:1meV) [3]. For a 2:1 stoichiometry and monoanions, there is one hole in the highest occupied molecular orbital of every other molecules, and the conduction band deriving from the overlap of the wave functions along the stacking direction becomes one quarter empty with holes (or equivalently, three quarter filled with electrons). Hence, it is the 1/4-filled Umklapp scattering which is relevant [4].Once an intra-stack dimerization is taken into account, two routes to insulating ground states are possible, and both are observed in the TMTTF compounds. For example, including the dimerization in the g-ology approach to the physics of 1D conductors [5] results in a localization of charges on the bonds between adjacent molecules due to 1/2-filled Umklapp scattering [6]. The ground state is referred to as a dimer-Mott insulator [7]; in the real materials, spin-Peierls (SP) or antiferromagnetic (AF) ordering occurs at low temperature [8].However, experiments reveal also a 4k F modulated charge density [9,10], which is stabilized by strong near-neighbor Coulomb repulsion [11,12]. Such a charge ordered (CO) configuration tends to favor an AF ground state, but here the exchange integrals, and consequently the AF wavevector, are controlled by the CO order parameter.The details of the T /P phase diagram for the TMTTF compounds clearly involve a mutual competition between these two effects [13] and the kinetic energy [14]. The opportunity to study the prog...

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We report electric field induced phase displacements of the charge density wave (CDW) in a single crystal of NbSe3 using 93Nb NMR spin-echo spectroscopy. CDW polarizations in the pinned state induced by unipolar and bipolar pulses are linear and reversible up to at least E = (0.96)ET. The polarizations have a broad distribution extending up to phase angles of order 60 degrees for electric fields close to threshold. No evidence for polarizations in excess of a CDW wavelength or for a divergence in polarization near ET are observed. The results are consistent with elastic depinning models, provided that the critical regime expected in large systems is not observable.