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Absence of magnetic order for the spin-half Heisenberg antiferromagnet on the star lattice

2004; American Physical Society; Volume: 70; Issue: 17 Linguagem: Inglês

10.1103/physrevb.70.174454

1550-235X

Johannes Richter, J. Schulenburg, A. Honecker, D. Schmalfuß,

High-pressure geophysics and materials

We study the ground-state properties of the spin-half Heisenberg antiferromagnet on the two-dimensional star lattice by spin-wave theory, exact diagonalization, and a variational mean-field approach. We find evidence that the star lattice is (besides the kagom\'e lattice) a second candidate among the 11 uniform Archimedean lattices where quantum fluctuations in combination with frustration lead to a quantum paramagnetic ground state. Although the classical ground state of the Heisenberg antiferromagnet on the star lattice exhibits a huge nontrivial degeneracy like on the kagom\'e lattice, its quantum ground state is most likely dimerized with a gap to all excitations. Finally, we find several candidates for plateaux in the magnetization curve as well as a macroscopic magnetization jump to saturation due to independent localized magnon states.