Unequal on-site interaction effects in the one-dimensional electron system at quarter filling

The one-dimensional antiferromagnetic correlated electron system described by the unusual t – U – J model with alternating on-site interactions at odd ( U o ) and even ( U e ) sites is studied analytically. At weak coupling, the use of bosonization and renormalization-group techniques helps to obtain ground-state phase diagram. At quarter filling, the unequal on-site repulsion ( U e ≠ U o ) causes the occurrence of umklapp processes and the generation of a charge excitation gap. Contrary to the usual case ( U e = U o ), the system is not metallic but insulating. For U e + U o < 2 J , the system is in a spin-gapped phase with charge-density-wave (CDW) instability; for U e + U o ≥ 2 J , the system is in a spin-gapless phase characterized by the coexistence of both CDW and spin-density-wave (SDW) instabilities, where the SDW correlation dominates over the CDW one.