The one-dimensional t-J model coupled to adiabatic phonons: A numerical   investigation
  The ground state of the one-dimensional t-J model coupled with phonons in the adiabatic limit is numerically investigated by use of the Lanczos technique at quarter filling. Due to the interplay between the electron-electron Coulomb repulsion and electron-phonon interaction, this model shows a sequence of lattice distortions leading to the formation of charge-density-waves and bond-order-waves. Moderate electron-electron and electron-lattice coupling may lead to coexistence of dimerization and tetramerization in the distortion pattern. Dimerization leads to the formation of an "antiferromagnetic" Mott insulator, while tetramerization gives rise to a spin-Peierls phase. By increasing the super-exchange coupling, antiferromagnetism is inhibited due to the change of the distortion periodicity. 
Samuele Bissola and Alberto Parola (Dipartimento di Fisica e   Matematica, Universita' dell'Insubria, Via Valleggio 11 Como,...