Tuning the bond-order wave phase in the half-filled extended Hubbard model

Theoretical and computational studies of the quantum phase diagram of the one-dimensional half-filled extended Hubbard model (EHM) indicate a narrow bond-order wave (BOW) phase with finite magnetic gap E-m for on-site repulsion U < U-*, the critical point, and nearest-neighbor interaction V-c approximate to U/2 near the boundary of the charge-density wave (CDW) phase. Potentials with more extended interactions that retain the EHM symmetry are shown to have a less cooperative CDW transition with higher U-* and wider BOW phase. Density-matrix renormalization group is used to obtain E-m directly as the singlet-triplet gap, with finite E-m marking the BOW boundary V-s(U). The BOW/CDW boundary V-c(U) is obtained from exact finite-size calculations that are consistent with previous EHM determinations. The kinetic energy or bond order provides a convenient new estimate of U-* based on a metallic point at V-c(U) for U < U-*. Tuning the BOW phase of half-filled Hubbard models with different intersite potentials indicates a ground state with large charge fluctuations and magnetic frustration. The possibility of physical realizations of a BOW phase is raised for Coulomb interactions.