New SDW phases in quasi-one-dimensional systems dimerized in the transverse direction

The spin density wave instabilities in the quasi-one-dimensional metal (TMTSF)2ClO4 are studied in the framework of a matrix random phase approximation for intraband and interband order parameters. Depending on the anion ordering potential V which measures the lattice doubling in the transverse direction, two different instabilities are possible. The SDW0 state at low values of V is antiferromagnetic in the b direction and has a critical temperature that decreases rapidly with V. The degenerated states SDW$_{\pm}$, stable at higher values of V, are superpositions of two magnetic orders, each one on its sub-family of chains. As V increases, the ratio between the two components of SDW$_{\pm}$ tends to zero and the critical temperature increases asymptotically towards that of SDW instability for a system having perfect nesting and no anion order. At intermediate V, i.e. between the phases SDW0 and SDW$_{\pm}$, the metallic state can persist down to T=0.