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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.
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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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