Effective Hamiltonian and low-lying eigenenergy clustering patterns of four-sublattice antiferromagnets

N.G. Zhang, C.L. Henley, C. Rischel, K. Lefmann

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    We study the low-lying eigenenergy clustering patterns of quantum antiferromagnets with p sublattices (in particular p = 4). We treat each sublattice as a large spin, and using second-order degenerate perturbation theory, we derive the effective (biquadratic) Hamiltonian coupling the p large spins. In order to compare with exact diagonalizations, the Hamiltonian is explicitly written for a finite-size lattice, and it contains information on energies of excited states as well as the ground state. The result is applied to the face-centered-cubic Type-I antiferromagnet of spin 1/2, including second-neighbor interactions. A 32-site system is exactly diagonalized, and the energy spectrum of the low-lying singlets follows the analytically predicted clustering pattern.
    Original languageEnglish
    JournalPhysical Review B Condensed Matter
    Issue number6
    Pages (from-to)064427.1-064427.17
    Publication statusPublished - 2002

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