Effect of nearest neighbor repulsion on the low-frequency phase diagram of a quarter-filled Hubbard-Holstein chain

Abstract

We have studied the influence of nearest-neighbor ͑NN͒ repulsions on the low-frequency phase diagram of a quarter-filled Hubbard-Holstein chain. The NN repulsion term induces the apparition of two new long range ordered phases ͑one 4k F CDW for positive U eff ϭUϪ2g 2 / and one 2k F CDW for negative U eff ) that did not exist in the Vϭ0 phases diagram. These results are put into perspective with the newly observed charge ordered phases in organic conductors and an interpretation of their origin in terms of electron molecularvibration coupling is suggested.