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Hierarchical mean-field approach to the J1-J2 Heisenberg model on a square lattice

AutorIsaev, L.; Ortiz, G.; Dukelsky, Jorge
Fecha de publicaciónene-2009
EditorAmerican Physical Society
CitaciónPhysical Review - Section B - Condensed Matter 79(2): 024409 (2009)
ResumenWe study the quantum phase diagram and excitation spectrum of the frustrated J1-J2 spin-1/2 Heisenberg Hamiltonian. A hierarchical mean-field approach, at the heart of which lies the idea of identifying relevant degrees of freedom, is developed. Thus, by performing educated, manifestly symmetry-preserving mean-field approximations, we unveil fundamental properties of the system. We then compare various coverings of the square lattice with plaquettes, dimers, and other degrees of freedom, and show that only the symmetric plaquette covering, which reproduces the original Bravais lattice, leads to the known phase diagram. The intermediate quantum paramagnetic phase is shown to be a (singlet) plaquette crystal, connected with the neighboring Néel phase by a continuous phase transition. We also introduce fluctuations around the hierarchical mean-field solutions, and demonstrate that in the paramagnetic phase the ground and first excited states are separated by a finite gap, which closes in the Néel and columnar phases. Our results suggest that the quantum phase transition between Néel and paramagnetic phases can be properly described within the Ginzburg-Landau-Wilson paradigm.
Descripción14 pages, 17 figures, 2 appendix.-- PACS number(s): 05.30. d, 75.10.Jm, 64.70.Tg
Versión del editorhttp://dx.doi.org/10.1103/PhysRevB.79.024409
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