Volume 66, Number 4, May 2004
|Page(s)||559 - 564|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 May 2004|
First- and second-order phase transitions in the Holstein-Hubbard model
Department of Mathematics, Imperial College - London SW7 2BZ, UK
2 Department of Physics, Niigata University - Ikarashi, Niigata 950-2181, Japan
Accepted: 4 March 2004
We investigate metal-insulator transitions in the half-filled Holstein-Hubbard model as a function of the on-site electron-electron interaction U and the electron-phonon coupling g. We use several different numerical methods to calculate the phase diagram, the results of which are in excellent agreement. When the electron-electron interaction U is dominant, the transition is to a Mott insulator; when the electron-phonon interaction dominates, the transition is to a localized bipolaronic state. In the former case, the transition is always found to be second order. This is in contrast to the transition to the bipolaronic state, which is clearly first order for larger values of U. We also present results for the quasiparticle weight and the double occupancy as functions of U and g.
PACS: 71.10.Fd – Lattice fermion models (Hubbard model, etc.) / 71.30.+h – Metal-insulator transitions and other electronic transitions / 71.38.-k – Polarons and electron-phonon interactions
© EDP Sciences, 2004
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