Novel phase boundary in the field induced spin density wave state in (TMTSF)2PF6

Magnetoresistance measurements on the quasi one-dimensional organic conductor (TMTSF)2PF6 performed in magnetic fields B up to 16 T, temperatures T down to 0.12 K, and under pressures P up to 1.4 GPa have revealed new phase boundary on the P–B–T phase diagram. The boundary subdivides the field induced spin density wave (FISDW) phase diagram into two regions. The low-temperature region of the FISDW diagram is characterized by a hysteresis behavior of the resistance R(B) which was observed in earlier studies and is typical for the first-order transitions. In contrast to the common believe, in the high temperature region of the FISDW phase diagram, the hysteresis in R(B) and, hence, the first-order transitions vanish. Nevertheless, sharp changes in dR/dB are observed both in the low and high temperature domains indicating that the transitions between different sub-phases exist over all range of the FISDW state. We compare these results with a theoretical prediction.