Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 32: Theoretische Modelierung von Materialien mit korrelierten Elektronen
TT 32.10: Vortrag
Freitag, 12. März 2004, 12:30–12:45, H18
Charge ordering in quarter filled ladder systems coupled to the lattice — •H.G. Evertz1, M. Aichhorn1, M. Hohenadler1, C. Gabriel1, J. Spitaler2, C. Ambrosch-Draxl2, and E.Ya. Sherman1 — 1Theor. Physik, TU Graz, Austria — 2Theor. Physik, KFU Graz, Austria
Using DMRG, Exact Diagonalization, and QMC, we investigate charge ordering in the presence of electron-phonon coupling for quarter-filled ladder systems. Parameters of a corresponding extended Hubbard model are obtained from first-principles band-structure calculations for NaV2O5.
We show that dynamical Holstein phonons, which are strong in NaV2O5, together with the nearest-neighbor Coulomb repulsion V result in a static zig-zag lattice distortion. Such a distortion, as also measured in NaV2O5, causes the system to order already at small values of V. We calculate dynamical susceptibilities, including spin and charge spectra and examine the effective Heisenberg model along the ladder in the ordered state. Energy and length of kink-like excitations of the ordered state are determined.
On finite systems, charge ordering also takes place as an effective finite temperature transition because of a rapidly growing correlation length. In a grand canonical ensemble, the charge order manifests itself as a plateau in the density as a function of chemical potential. In ongoing calculations, we are investigating Raman spectra and the effects of interladder coupling.