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TT: Fachverband Tiefe Temperaturen
TT 48: CE: Metal-Insulator Transition 2
TT 48.6: Vortrag
Donnerstag, 17. März 2011, 12:00–12:15, HSZ 105
Effective spin Hamiltonian for the spin liquid of the Hubbard model on the honeycomb lattice — •Hong-Yu Yang1, Andreas Läuchli2, and Kai Phillip Schmidt1 — 1Lehrstuhl für Theoretische Physik I, TU Dortmund, 44221 Dortmund, Germany — 2MPI PKS, Nöthnitzerstr. 38, 01187 Dresden, Germany
Motivated by the spin liquid phase unveiled by quantum Monte Carlo simulations of the Hubbard model on the honeycomb lattice at intermediate values of U, we derive the effective spin-only model from the strong-coupling limit using continuous unitary transformations (CUTs). It turns out that the spin liquid phase is located in the non-perturbative regime. We therefore apply a recently developped non-perturbative extension of CUTs named graph-based CUT (gCUTs) in order to obtain a pure spin model as effective Hamiltonian for the intermediate U regime. We use exact diagonalizations to check the validity of the effective spin model by comparing its low-energy properties to the one of the Hubbard model on small clusters. Surprisingly, we find that besides a frustrating next-nearest neighbor two-spin exchange a family of six-spin interactions are the dominant corrections to the nearest-neighbor Heisenberg model.