Commensurability effects in the magnetoresistance of (TMTSF)₂PF₆

We present a study of the angular dependence of the magnetoresistance of the quasi-one-dimensional organic conductor (TMTSF)₂PF₆. For some special orientations of magnetic field in the least-conducting plane, a commensurability effect in the electronic open-orbit motion is expected. At these special "magic angles", dips in the resistance along the least-conducting axis in both metallic and field-induced-spin-density-wave (FISDW) states are detected. In the latter states, the dips gradually fade away with the increasing field. Moreover, the commenusurability effect intereferes directly with FISDW transitions: For magic angles, the threshold field goes through a weak minimum and the amplitude of the FISDW magnetoresistance oscillations is diminished.