Nonperturbative effects of the periodic potential on the field-induced spin-density wave and the sign of the quantum Hall effect in the quasi-one-dimensional conductor (TMTSF)2ClO4

We show that in (TMTSF)(2)ClO4 the field-induced spin-density wave (FISDW) with negative quantum number (N=-2) of the nesting vector is stabilized in some region in the parameters of magnetic field and the strength of the anion potential, which corresponds to the very recently observed phase diagram of (TMTSF)(2)ClO4 in the parameter plane of magnetic field vs cooling rate by Matsunaga [J. Phys. IV 131, 269 (2005)]. The spin-density wave is induced by the magnetic field in the quasi-one-dimensional conductors such as (TMTSF)(2)PF6 and (TMTSF)(2)ClO4. The wave vector of the FISDW is quantized and the Hall conductivity is quantized corresponding to the quantum number (N) of the wave vector. In (TMTSF)(2)ClO4, the ordering of the anion ClO4 makes the periodic potential, which has been known to drastically affect the FISDW. We study the instability to the FISDW by taking the eigenstates in the magnetic field numerically, with the periodic potential being treated nonperturbatively. We obtain the phase diagram of the quantum number N for FISDW in the quasi-one-dimensional systems in the parameter plane of magnetic field and the strength of the periodic potential, which can be controlled by the cooling rate.