Insulating Phases Driven By Unequal On-Site Repulsion In The 1d Unconventional Hubbard Model

The one-dimensional unconventional Hubbard model with alternating on-site interaction at odd (U-o) and even (U-e) lattice sites is analytically studied in the weak-coupling regime. The existence of unequal on-site repulsion (U-o not equal U-e) makes a dramatic impact on the charge excitation behavior in one dimension. At quarter filling, the alternating Hubbard interaction leads to the occurrence of umklapp processes and to the generation of a charge gap. As usual, the low-energy spin excitation is still massless. The ground state shows insulating behavior, characterized by the coexisting spin-density-wave and charge-density-wave instabilities.