Theory of the high field phase in (TMTSF)(2)ClO4 under anion ordering

Stimulated by a recent experiment on (TMTSF)(2)ClO4, reporting a new phase diagram with a first order transition line at the high field, the field induced spin density wave (FISDW) states are reexamined under the anion ordering. It is found that a new type of FISDW state, which differs from that described by the so-called standard theory, is stabilized. We interpret the first order line as arising from a transition between the new state and the standard one when H is varied.