Ground-state phase diagram of the unconventional Hubbard chain with bond–charge interaction

Abstract

Using the field-theory approach combining bosonization and renormalization group, we investigate the weak-coupling phase diagram of the unconventional Hubbard chain, where in addition to a bond–charge interaction (X), the Hubbard interaction differs between odd (Uo) and even (Ue) sites. The result shows that at quarter filling, the unequal Hubbard repulsion has a great influence on low-energy charge excitations. For the attractive X, the umklapp scattering always exists, and the ground state only exhibits a spin-gapless insulating phase with dominant spin-density-wave correlations. For the repulsive X, the umklapp processes only take place if both Uo and Ue are greater than 8Xcos(π/4), and the phase diagram consists of three phases, a metallic phase with the spin-gapped singlet superconducting correlation, and two insulating phases characterized by the spin-density-wave and charge-density-wave correlations. We also present the phase diagram of the standard t-U-X chain in the case of non-half filling.

Keywords

• Phase diagram
• Unconventional Hubbard chain
• Quarter filling
• Bond–charge interaction
• Weak coupling