Abstract
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_ene 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<2J, the system is in a spin-gapped phase with charge-density-wave (CDW) instability; for U_e+U_oge 2J, 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.
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