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Brisures de symétrie dans les Hamiltoniens de Heisenberg classiques et quantiques en deux dimensions

Abstract : Following recent experiments on an S=1/2 antiferromagnet on the kagomé lattice, we investigated the J1-J2 Heisenberg model with ferromagnetic J1 and antiferromagnetic J2. Classically the ground state displays 12-sublattices Néel long-range order which fully breaks the symmetry of the Hamiltonian at T=0. The non-coplanarity of the order parameter induces a chiral symmetry breaking which is restored at finite temperature, together with the proliferation of the relevant Z2 vortices. The first order pattern of the chiral transition goes weaker and weaker as the frustration J2/|J1| increases. For spins 1/2, quantum fluctuations renormalize the classical order without wiping it out, as far as J2/|J1|<3. With stronger frustration, quantum fluctuations restore the SO(3) symmetry and one obtains a gapped phase. We also studied the influence of cyclic four-spins exchange on the square lattice, obtaining the first numerical evidence for a p-nematic order for spins 1/2.
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https://tel.archives-ouvertes.fr/tel-00010943
Contributor : Jean-Christophe Domenge <>
Submitted on : Wednesday, November 9, 2005 - 7:46:03 PM
Last modification on : Wednesday, December 9, 2020 - 3:11:27 PM
Long-term archiving on: : Friday, April 2, 2010 - 11:06:29 PM

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  • HAL Id : tel-00010943, version 1

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Jean-Christophe Domenge. Brisures de symétrie dans les Hamiltoniens de Heisenberg classiques et quantiques en deux dimensions. Matière Condensée [cond-mat]. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00010943⟩

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