Coexistence of charge-density waves, bond-order waves, and spin-density waves in quasi-one-dimensional charge-transfer salts

Charge, spin, as well as lattice instabilities are investigated in isolated or weakly coupled chains of correlated electrons at quarter filling. Our analysis is based on extended Hubbard models including nearest-neighbor repulsion and Peierls coupling to lattice degrees of freedom. While treating the electronic quantum fluctuations exactly, the lattice structure is optimized self-consistently. We show that, generically, isolated chains undergo instabilities towards coexisting charge-density waves (CDW's) and bond order waves (BOW's) insulating spin-gapped phases. The spin and charge gaps of the BOW-CDW phase are computed. In the presence of an interchain magnetic coupling spin-density waves phases including a CDW or a BOW component are also found. Our results are discussed in the context of insulating charge-transfer salts.