Metallicity in the half-filled Holstein-Hubbard modelH. Fehske1, G. Hager2 and E. Jeckelmann3
1 Institute for Physics, Ernst-Moritz-Arndt University Greifswald - D-17487 Greifswald, Germany, EU
2 Computing Center, Friedrich-Alexander University Erlangen-Nürnberg - D-91058 Erlangen, Germany, EU
3 Institute for Theoretical Physics, Leibniz University Hannover - D-30167 Hannover, Germany, EU
received 6 August 2008; accepted in final form 21 October 2008; published December 2008
published online 24 November 2008
We re-examine the Peierls insulator to Mott insulator transition scenario in the one-dimensional Holstein-Hubbard model where, at half-filling, electron-phonon and electron-electron interactions compete for establishing charge- and spin-density-wave states, respectively. By means of large-scale density-matrix renormalization group calculations we determine the spin, single-particle and two-particle excitation gaps and prove —in the course of a careful finite-size scaling analysis— recent claims for an intervening metallic phase in the weak-coupling regime. We show that for large phonon frequencies the metallic region is even more extended than previously expected, and subdivided into ordinary Luttinger-liquid and bipolaronic-liquid phases.
71.30.+h - Metal-insulator transitions and other electronic transitions.
71.10.Hf - Non-Fermi-liquid ground states, electron phase diagrams and phase transitions in model systems.
71.38.-k - Polarons and electron-phonon interactions.
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