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TT: Tiefe Temperaturen

TT 11: Postersitzung II (Metall-Isolator-Überg
änge, Phasenüberg
änge in Quantensystemen, Theorie: Systeme korrelierter Elektronen)

TT 11.43: Poster

Tuesday, March 25, 2003, 14:30–19:00, P2c, P2d

Quadrumer phase of the crossed spin-chain model — •Wolfram Brenig and Matthias Grzeschik — Institut für Theoretische Physik, Technische Universität Braunschweig, Germany

Starting from the limit of isolated quadrumers we discuss the magnetism of the frustrated spin-1/2 crossed chain model which generalizes the planar pyrochlore to the case of mixed inter-plaquette exchange j₁ and j₂. Performing a series expansion with respect to the latter exchange couplings by using continuous unitary transformations we compute the ground state energy, as well as the elementary triplet and singlet excitations. The triplet dispersion is found to be very sensitive to the frustration. The instability of the quadrumer valence-bond-solid towards the formation of either a sliding Luttinger liquid or long-range antiferromagnetic order is detailed. Finally a comparison to results from exact diagonalization will be given.