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|Type:||Artigo de periódico|
|Title:||Plaquette valence-bond solid in the square-lattice J(1)-J(2) antiferromagnet Heisenberg model: A bond operator approach|
|Abstract:||We study the plaquette valence-bond solid phase of the spin-1/2J(1)-J(2) antiferromagnet Heisenberg model on the square lattice within the bond-operator theory. We start by considering four S = 1/2 spins on a single plaquette and determine the bond operator representation for the spin operators in terms of singlet, triplet, and quintet boson operators. The formalism is then applied to the J(1)-J(2) model and an effective interacting boson model in terms of singlets and triplets is derived. The effective model is analyzed within the harmonic approximation and the previous results of Zhitomirsky and Ueda [Phys. Rev. B 54, 9007 (1996)] are recovered. By perturbatively including cubic (triplet-triplet-triplet and singlet-triplet-triplet) and quartic interactions, we find that the plaquette valence-bond solid phase is stable within the parameter region 0.34 < J(2)/J(1) < 0.59, which is narrower than the harmonic one. Differently from the harmonic approximation, the excitation gap vanishes at both critical couplings J(2) = 0.34J(1) and J(2) = 0.59J(1). Interestingly, for J(2) < 0.48J(1), the excitation gap corresponds to a singlet-triplet excitation at the Gamma point while, for J(2) > 0.48J(1), it is related to a singlet-singlet excitation at the X = (pi/2,0) point of the tetramerized Brillouin zone.|
|Editor:||Amer Physical Soc|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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