Abstract
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 language | English |
---|---|
Journal | Physical Review B Condensed Matter |
Volume | 65 |
Issue number | 6 |
Pages (from-to) | 064427.1-064427.17 |
ISSN | 0163-1829 |
DOIs | |
Publication status | Published - 2002 |