MAGNETIC-FIELD DEPENDENCE OF THE PHASE-COHERENCE LENGTH IN THE SPIN-DENSITY-WAVE STATE OF TETRAMETHYLTETRASELENAFULVALINIUM NITRATE, (TMTSF)2NO3

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)2NO3. 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.