arXiv:cond-mat/0611415 · Physical Review B
Band-insulator–metal–Mott-insulator transition in the half-filled t−t′ ionic Hubbard chain
G. I. Japaridze, R. Hayn, P. Lombardo, E. Müller‐Hartmann
Abstract
We investigate the ground-state phase diagram of the half-filled $t\text{\ensuremath{-}}{t}^{\ensuremath{'}}$ repulsive Hubbard model in the presence of a staggered ionic potential $\ensuremath{\Delta}$ using the continuum-limit bosonization approach. We find that with increasing on-site repulsion $U$, depending on the value of the next-nearest-neighbor hopping amplitude ${t}^{\ensuremath{'}}$, the model shows three different versions of the ground-state phase diagram. For ${t}^{\ensuremath{'}}<{t}_{c}^{{*}^{\ensuremath{'}}}$, the ground-state phase diagram consists of the following three insulating phases: band insulator at $U<{U}_{c}$, ferroelectric insulator at ${U}_{c}<U<{U}_{s}$, and correlated (Mott) insulator at $U>{U}_{c}$. For ${t}^{\ensuremath{'}}>{t}_{c}^{\ensuremath{'}}$ there is only one transition from a spin-gapped metallic phase at $U<{U}_{c}$ to a ferroelectric insulator at $U>{U}_{c}$. Finally, for intermediate values of the next-nearest-neighbor hopping amplitude ${t}_{c}^{{*}^{\ensuremath{'}}}<{t}^{\ensuremath{'}}<{t}_{c}^{\ensuremath{'}}$ we find that with increasing on-site repulsion, at ${U}_{c1}$ the model undergoes a second-order commensurate-incommensurate-type transition from a band insulator into a metallic state and at larger ${U}_{c2}$ there is a Kosterlitz-Thouless-type transition from a metal to a ferroelectric insulator.