One-dimensional spinless fermion model with competing interactions beyond half-filling

An accurate numerical consideration of 1D spinless fermion model with next-nearest neighbour (NNN) interactions is carried out for the electron concentrations 4/7. It is shown that depending on the parameters of the model it can be either Luttinger liquid or bipolaron liquid. In the former case competing interactions can result in a smooth behavior of one-electron distribution function at the Fermi surface with a divergence in the second derivative with respect to the quasimomentum (and not in the first one, as usual). In this connection, uncommon photoemission spectra for some 1D conductors can be explained qualitatively. PACS 71.10.Pm, 71.10.Fd Frustrations and competing interactions are very important for strongly correlated electron systems. As it was shown in a seminal work[1] they can change drastically a ground state of quantum antiferromagnets leading to the formation of “resonating valence bond” (RVB), or quantum spin liquid, state (see also [2] and references therein). This state has been found later in a series of compounds with both magnetic (spin liquid) and charge (pseudospin liquid) degrees of freedom, see, e.g., the discussion in Refs.[3, 4].The effects of competing interactions were investigated recently for one-dimensional (1D) spinless fermion model[5, 6, 7]. Usually this model is used for the description of Verwey metal-insulator transitions and charge ordering phenomena in Fe3O4, Ti4O7 and other d-metal compounds[8, 9, 10]. It is expected that in the half-filled case the growth of the Coulomb interaction leads to the transition from the metallic state to the insulating charge-ordered one. It appeared, however, that the competing interactions can result in the stabilization of metallic phase without charge ordering for arbitrarily strong Coulomb interaction[5, 6], this phase being not usual (for 1D systems) Luttinger liquid[7]. Here we investigate this model beyond half-filling. We proceed with the Hamiltonian