Bond-located ordering in the one-dimensional Penson-Kolb-Hubbard model

In this paper we study the ground-state phase diagram of the one-dimensional half-filled repulsive (U > 0) Hubbard model supplemented with the pair-hopping interaction (W) (the Penson-Kolb-Hubbard model) using the continuum-limit field theory approach. We compare the low-energy properties of the U > 0 Hubbard model and W > 0 Penson-Kolb model. We show that, despite similar excitation spectra, the character of instabilities in these models is completely different. In contrast to the Hubbard model, in the case of the Penson-Kolb model, the dynamical generation of a charge gap leads to the suppression of spin-density-wave (SDW) fluctuations. The charge-density-wave fluctuations survive and coexist with bond-located SDW (Bd-SDW) instabilities. The Bd-SDW corresponds to a magnetically ordered state with staggered magnetization located on bonds between sites. The possibility of bond-located ordering is connected with the site-off-diagonal nature of the pair-hopping interaction. In the case of PKH the bond-ordered states exist at \W\ > U/2. For W > U/2 the Bd-SDW is realized while for W < -U/2 the dimerized phase is realized.