Hamburg 2001 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 11: Fachsymposium: Eindimensionale Übergangsmetalle

TT 11.6: Hauptvortrag

Dienstag, 27. März 2001, 17:00–17:30, A

Quantum Monte Carlo Simulations of Low-Dimensional Transition Metal Oxides — •Matthias Troyer — Theoretische Physik, ETH Zürich, CH-8093 Zürich, Sitzerland

Unusual magnetic phenomena are observed in quasi one-dimensional transition metal oxides. In ladder structures, consisting of two coupled chains. Quantum fluctuations create a resonating valence bond state with short range magnetic order and a finite gap for spin triplet excitations. Quantum Monte Carlo simulations can not only qualitatively explain this behavior, but allow quantitative comparisons to experimental measurements, and thus a determination of the microscopic coupling parameters in the spin gap compound SrCu₂O₃ and the nearly quantum critical material LaCuO_2.5 . More complicated frustrated lattice structures are present in vanadates. There we used a combination of ab-initio LDA+U calculations and quantum Monte Carlo simulations to explain unusual magnetic properties. In particular we could determine why there is a huge spin gap in CaV₂O₅ but only a small or vanishing gap in MgV₂O₅, explain the unusual magnetic ordering in CaV₃O₇ and clarify the origin of the plaquette RVB state in CaV₄O₉. In the related spin-Peierls compound NaV₂O₅ quantum Monte Carlo simulations allow the determination of the temperature dependence of the spin gap.