Charge ordering in quarter-filled ladder systems coupled to the lattice

M. Aichhorn, M. Hohenadler, E. Ya. Sherman, J. Spitaler, C. Ambrosch-Draxl, and H. G. Evertz
Phys. Rev. B 69, 245108 – Published 17 June 2004

Abstract

We investigate charge ordering in the presence of electron-phonon coupling for quarter-filled ladder systems by using exact diagonalization. As an example we consider NaV2O5 using model parameters obtained from first-principles band-structure calculations. The relevant Holstein coupling to the lattice considerably reduces the critical value of the nearest-neighbor Coulomb repulsion at which formation of the zig-zag charge-ordered state occurs, which is then accompanied by a static lattice distortion. Energy and length of a kink-like excitation on the background of the distorted lattice are calculated. Spin and charge spectra on ladders with and without static distortion are obtained, and the charge gap and the effective spin-spin exchange parameter J are extracted. J agrees well with experimental results. Analysis of the dynamical Holstein model, restricted to a small number of phonons, shows that low frequency lattice vibrations have a strong influence on the charge ordering, particularly in the vicinity of the phase transition point. By investigating the charge order parameter we conclude that phonons produce dynamical zig-zag lattice distortions. A model with only static distortions gives a good description of the system well away from the transition point while overestimating the amount of charge ordering in the vicinity of the phase transition.

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  • Received 19 December 2003

DOI:https://doi.org/10.1103/PhysRevB.69.245108

©2004 American Physical Society

Authors & Affiliations

M. Aichhorn1, M. Hohenadler1, E. Ya. Sherman1,2, J. Spitaler2, C. Ambrosch-Draxl2, and H. G. Evertz1

  • 1Institut für Theoretische Physik, Technische Universität Graz, Petersgasse 16, A-8010 Graz, Austria
  • 2Institut für Theoretische Physik, Karl-Franzens-Universität Graz, Universitätsplatz 5, A-8010 Graz, Austria

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Issue

Vol. 69, Iss. 24 — 15 June 2004

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