HIGH-FIELD MAGNETORESISTANCE OF THE BECHGAARD SALT (TMTSF)(2)NO3 - QUANTUM OSCILLATIONS IN THE SPIN-DENSITY-WAVE STATE AND PHASE-TRANSITIONS

The transverse magnetoresistance of the Bechgaard salt (TMTSF)(2)NO3 h as been measured up to 37 T at ambient pressure in the temperature ran ge from 2 to 77 K. When the magnetic field is parallel to the lowest c onductivity direction c and for temperatures higher than similar to 1 2 K, the data can be accounted for by a power law, the exponent of whi ch decreases as the anion ordering takes place. At lower temperatures, the magnetic field increases the spin-density-wave (SDW) transition t emperature, 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-inde pendent 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 c direct ion or on the other. The oscillation data are discussed on the basis o f recent calculations of Yakovenko.