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Phase diagram of the one-dimensional Hubbard-Holstein model at half and quarter filling
Physical Review B
  • Rahul Hardikar, Butler University
  • R. T. Clay
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The Hubbard-Holstein model is one of the simplest to incorporate both electron-electron and electron-phonon interactions. In one dimension at half filling, the Holstein electron-phonon coupling promotes on-site pairs of electrons and a Peierls charge-density wave, while the Hubbard on-site Coulomb repulsion U promotes antiferromagnetic correlations and a Mott insulating state. Recent numerical studies have found a possible third intermediate phase between Peierls and Mott states. From direct calculations of charge and spin susceptibilities, we show that (i) as the electron-phonon coupling is increased, first a spin gap opens, followed by the Peierls transition. Between these two transitions, the metallic intermediate phase has a spin gap, no charge gap, and properties similar to the negative-U Hubbard model. (ii) The transitions between Mott/intermediate and intermediate/Peierls states are of the Kosterlitz-Thouless form. (iii) For larger U, the two transitions merge at a tricritical point into a single first-order Mott/Peierls transition. In addition, we show that an intermediate phase also occurs in the quarter-filled model.

This article was archived with permission from APS Physics. Article also available from Physical Review B.
Citation Information
Rahul Hardikar and R. T. Clay. "Phase diagram of the one-dimensional Hubbard-Holstein model at half and quarter filling" Physical Review B Vol. 75 (2007)
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