Two rapid oscillations in the magnetoresistance in the field-induced spin-density-wave state of (TMTSF)(2)ClO4

We report a systematic study of longitudinal and transverse magnetoresistan ce in the quasi-one-dimensional organic conductor (TMTSF)(2)ClO4. We found two distinctly different quantum (rapid) oscillations (RO's) at different t emperature regions in the field-induced spin-density-wave (FISDW) phase. Fo r temperature sweeps in a fixed held, a resistance peak is observed at T* w hich depends on the field. Surprisingly, the type of RO is correlated with T*(H). The difference between two oscillations leads us to establish subpha ses in the main FISDW phase of (TMTSF)(2)ClO4. We also found the low-field boundary of McKernan's 3.5 K phase from a sudden increase of resistance. Ou r results conclude that the separate SDW transition on each pair of the Fer mi surfaces is possibly responsible for subphases in the FISDW phase.