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Conductivity and permittivity of the quasi-one-dimensionsional organic transfer salt $(\mathrm{TMTTF}{)}_{2}{\mathrm{PF}}_{6}$ have been measured at low frequencies ${(10}^{3}\char21{}{10}^{7}\mathrm{Hz})$ between room temperature down to below the temperature of transition into the spin-Peierls state. We interpret the huge real part of the dielectric permittivity (up to ${10}^{6})$ in the localized state as the realization in this compound of a charge ordered state of Wigner crystal type due to long-range Coulomb interaction.

The transverse magnetoresistance of the Bechgaard salt (TMTSF)[sub 2]NO[sub 3] has been measured up to 37 T at ambient pressure in the temperature range from 2 to 77 K. When the magnetic field is parallel to the lowest conductivity direction [ital c][sup *] and for temperatures higher than [similar to]12 K, the data can be accounted for by a power law, the exponent of which decreases as the anion ordering takes place. At lower temperatures, the magnetic field increases the spin-density-wave (SDW) transition temperature, in overall agreement with theoretical predictions for the imperfect-nesting case. Two oscillation series, both linked to the SDW state, have been observed in the 2--10 K range. Their temperature-independent frequencies, measured from 2 to 8 K, are at (63[plus minus]2) and (248[plus minus]5) T, respectively. These oscillations have been studied (at 4.2 K) as a function of the field direction. They were found to deviate from the two-dimensional model since, in particular, their behavior differs according to whether the field is tilted on one side of the [ital c][sup *] direction or on the other. The oscillation data are discussed on the basis of recent calculations of Yakovenko.

We have observed a clear series of fine structures superposed on the angular dependence of the transverse magnetoresistance in the semimetallic spin-density-wave state of the organic conductor (TMTSF${)}_{2}$${\mathrm{NO}}_{3}$. They appear at the positions defined by the strength of the field component parallel to the least-conduction direction (B cos \ensuremath{\theta}\ensuremath{\simeq}const). An observed asymmetry in the magnitude is due to the striking angular dependence of the oscillations amplitude. The frequency of the oscillations (${\mathit{B}}_{\mathit{S}}$=63 T) is close to the frequency of the field-induced spin-density-wave transitions found in the other Bechgaard salts. This oscillatory phenomenon is considered to result from the orbit quantization inside the closed parts of the Fermi surface which are due to the 2${\mathit{k}}_{\mathit{F}}$ anion ordering together with the imperfect spin-density-wave nesting.

We have used electric-field-dependent measurements to probe the magnetic-field dependence of the phase-coherence length in the spin-density-wave (SDW) state of the organic conductor tetramethyltetraselenafulvalinium nitrate (TMTSF${)}_{2}$${\mathrm{NO}}_{3}$. The threshold electric field increases if a magnetic field is applied in the plane perpendicular to the highly conducting axis. The magnitude of the increase is angle-dependent and vanishes when the field is applied along the intermediate-conductivity axis. This behavior results from a reduction of the phase-coherence length of the SDW with strongly imperfect nesting in a magnetic field.

Interlayer magnetoresistance of the Bechgaard salt (TMTSF)$_2$NO$_3$ is investigated up to 50 teslas under pressures of a few kilobars. This compound, the Fermi surface of which is quasi two-dimensional at low temperature, is a semi metal under pressure. Nevertheless, a field-induced spin density wave is evidenced at 8.5 kbar above $\sim$ 20 T. This state is characterized by a drastically different spectrum of the quantum oscillations compared to the low pressure spin density wave state.