Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 19: Correlated Electrons: Quantum-Critical Phenomena

TT 19.10: Vortrag

Dienstag, 26. Februar 2008, 16:30–16:45, H 3010

Breakdown of a valence bond solid in a Heisenberg model with four-spin interaction on honeycomb layers — •Thomas C. Lang^1,2, Anders W. Sandvik², and Fakher F. Assaad¹ — ¹Institut für Theoretische Physik und Astrophysik, Universität Würzburg, D-97074 Würzburg, Germany — ²Department of Physics, Boston University, Boston, MA 02115, USA

We investigate the scenario of the breakdown of a valence bond solid (VBS) in an S = 1/2 quantum antiferromagnet with non-frustrating four-spin interaction on the single and bilayer hexagonal lattice. By means of quantum Monte Carlo in the valence bond basis we find a strong first-order VBS-Néel phase transition in the single layer. In the bilayer the Néel regime separates the VBS and a disordered (zero tilted) phase by a continuous quantum phase transition. A quantum critical point marking a direct VBS-VBS or VBS-disorder transition is absent. This behavior is attributed to the lattice symmetry which allows rigid valence bond configurations to survive while spin-fluctuations are enhanced.