Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 42: Correlated Electrons: Low-dimensional Systems - Models 2
TT 42.5: Vortrag
Donnerstag, 26. März 2009, 15:00–15:15, HSZ 301
Effective models for Mott insulating phases in frustrated Hubbard models — •Hong-Yu Yang1, Andreas Laeuchli2, Frederic Mila3, and Kai Phillip Schmidt1 — 1Lehrstuhl für theoretische Physik I, TU Dortmund, 44221 Dortmund, Germany — 2Max Planck Institut für Physik komplexer Systeme, Nöthnitzerstr. 38, 01187 Dresden, Germany — 3Institute for theoretical Physics, Ecole Polytechnique Federale de Lausanne, 1015 Lausanne, Switzerland
We derive effective quantum spin models models for a frustrated t-t’Hubbard model on the square lattice using perturbative continuous unitary transformations. For large U the effective Hamiltonian at half filling contains only a nearest-neighbor Heisenberg interaction giving rise to long-range ordered antiferromagnetic phases. Limiting cases are the unfrustrated square lattice (t’=0) with a Neel ordered ground state and the triangular lattice (t’=t) having a 120-degree three-sublattice order. In the unfrustrated case it is known that corrections at finite U, e.g. ring-exchange couplings or Heisenberg interactions of longer range, do not destabilize the Neel-ordered ground state. Only in the limit of small U a metallic phase is stable. In this sense one has a hard Mott insulator. In our study we investigate the question whether corrections in the frustrated case stabilize an intermediate spin liquid phase between the long-range ordered antiferromagnetic phase at large U and the metallic phase at small U. This case would be called a soft Mott insulator. We tackle this problem by solving the effective model obtained by continuous unitary transformations using exact diagonalization.