Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet

Zheng, W., Fjaerestad, J. O., Singh, R. R. P., McKenzie, R. H. and Coldea, R. (2006) Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet. Physical Review B, 74 22: 224420-1-224420-13. doi:10.1103/PhysRevB.74.224420

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Author Zheng, W.
Fjaerestad, J. O.
Singh, R. R. P.
McKenzie, R. H.
Coldea, R.
Title Excitation spectra of the spin-1/2 triangular-lattice Heisenberg antiferromagnet
Journal name Physical Review B   Check publisher's open access policy
ISSN 1098-0121
Publication date 2006
Sub-type Article (original research)
DOI 10.1103/PhysRevB.74.224420
Open Access Status File (Publisher version)
Volume 74
Issue 22
Start page 224420-1
End page 224420-13
Total pages 13
Editor P. D. Adams
Place of publication College Pk
Publisher American Physical Society
Collection year 2006
Language eng
Subject C1
780102 Physical sciences
240203 Condensed Matter Physics - Electronic and Magnetic Properties; Superconductivity
Abstract We use series expansion methods to calculate the dispersion relation of the one-magnon excitations for the spin-(1)/(2) triangular-lattice nearest-neighbor Heisenberg antiferromagnet above a three-sublattice ordered ground state. Several striking features are observed compared to the classical (large-S) spin-wave spectra. Whereas, at low energies the dispersion is only weakly renormalized by quantum fluctuations, significant anomalies are observed at high energies. In particular, we find rotonlike minima at special wave vectors and strong downward renormalization in large parts of the Brillouin zone, leading to very flat or dispersionless modes. We present detailed comparison of our calculated excitation energies in the Brillouin zone with the spin-wave dispersion to order 1/S calculated recently by Starykh, Chubukov, and Abanov [Phys. Rev. B74, 180403(R) (2006)]. We find many common features but also some quantitative and qualitative differences. We show that at temperatures as low as 0.1J the thermally excited rotons make a significant contribution to the entropy. Consequently, unlike for the square lattice model, a nonlinear sigma model description of the finite-temperature properties is only applicable at temperatures < 0.1J. Finally, we review recent NMR measurements on the organic compound kappa-(BEDT-TTF)(2)Cu-2(CN)(3). We argue that these are inconsistent with long-range order and a description of the low-energy excitations in terms of interacting magnons, and that therefore a Heisenberg model with only nearest-neighbor exchange does not offer an adequate description of this material.
Keyword Physics, Condensed Matter
Frustrated Quantum Antiferromagnets
Finite-temperature Properties
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 09:52:41 EST