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TT: Tiefe Temperaturen
TT 6: Postersitzung I: Josephsonkontakte und SQUIDs, Supraleitung: Theorie, Korrelierte Elektronen, Niederdimensionale Systeme, Magnetotransport, Quantenhalleffekt, Kohlenstoff-Nanoröhrchen, Quantenflüssigkeiten
TT 6.27: Poster
Monday, March 26, 2001, 14:30–17:00, Rang S\ 3
Charge and Spin Ordering in the Extended t-U-V Hubbard Ladder — •Matthias Vojta1, Arnd Hübsch2, and Reinhard M. Noack3 — 1Theoretische Physik III, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg, D-86135 Augsburg — 2Institut für Theoretische Physik, Technische Universität Dresden, D-01062 Dresden — 3Institut für Physik, Johannes-Gutenberg-Universität Mainz, D-55099 Mainz
We investigate the phases and the charge-ordering transition in a two-leg Hubbard ladder with additional nearest-neighbor Coulomb repulsion, V, at zero temperature using the Density Matrix Renormalization Group technique. We consider electron densities between quarter and half filling. For quarter filling and U=8 t, we find evidence for a continuous phase transition between a homogeneous state at small V and a broken-symmetry state with “checkerboard” [wavevector Q=(π,π)] charge order at large V. This transition to a checkerboard charge-ordered state remains present at all larger fillings, but becomes discontinuous at sufficiently large filling. We discuss the influence of U/t on the transition and estimate the position of the tricritical points. At quarter filling, we study the spin dynamics in the charge-ordered state of the ladder. We establish the mapping of its spin degrees of freedom to a frustrated spin-1/2 chain, and make contact with the results known from one-dimensional frustrated Heisenberg and t-J models.