Field induced spin density wave phases in (TMTSF) ₂ClO ₄ at high magnetic field

Abstract
We propose a model to study the spin density wave (SDW) phases under a high magnetic field in the relaxed (TMTSF) ₂ClO ₄ salt where the ClO ^-₄ anions undergoe an orientational ordering transition. This opens a gap at the original Fermi surface and leads to a two band energy spectrum. We show that, in the high field regime, a competition takes place between the interband and the intraband SDW order parameters. We find that the intraband SDW component has always the highest critical temperature but it is due to two coexisting order parameters. This coexistence tends to destabilize the corresponding phase as the temperature decreases. Eventually, a first order transition takes place from the original SDW phase to a new phase originating from interband processes. The obtained results agree with the experimental phase diagram. Key words. Organic conductors - Spin-density wave - Quantum Hall effect