Lebed resonance effects in the metallic and spin-density-wave phases of (TMTSF)₂PF₆

The angular dependence of the magnetoresistance along the least conducting axis has been investigated in both metallic and field-induced spin-density-wave (FISDW) states of the quasi-one-dimensional organic conductor (TMTSF)₂PF₆. Strong dips in the resistance occur for Lebed’s «magic» field orientations associated to resonant effects in the open-orbit electron motion. The dips exist in both the metallic and the FISDW states but gradually fade away with increasing field in the latter state. The study of the FISDW phase transitions as a function of field orientation confirms the existence of a minimum for the threshold field in the vicinity of a magic angle. Such an anomaly is not observed in the angular dependence of successive transition fields within the FISDW state.