High-field magnetoresistance of the Bechgaard salt (TMTSF)2NO3: Quantum oscillations in the spin-density-wave state and phase transitions

The transverse magnetoresistance of the Bechgaard salt (TMTSF${)}_2$ ${\mathrm{NO}}_3$ 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 ${\mathit{c}}^{\mathrm{*}}$ and for temperatures higher than ∼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±2) and (248±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 ${\mathit{c}}^{\mathrm{*}}$ direction or on the other. The oscillation data are discussed on the basis of recent calculations of Yakovenko.