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

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 roton-like 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 [cond-mat/0608002]. 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 non-linear sigma model description of the finite-temperature properties is only applicable at extremely low temperatures.

14 pages, 11 figures

References in corpus (7)

• U(1) Gauge Theory of the Hubbard Model : Spin Liquid States and Possible Application to k-(BEDT-TTF)_2 Cu_2 (CN)_3
• Emergence of inhomogeneous moments from spin liquid in the triangular-lattice Mott insulator $\kappa$-(ET)${}_2$Cu${}_2$(CN)${}_3$
• Magnon Decay in Noncollinear Quantum Antiferromagnets
• Flat spin wave dispersion in a triangular antiferromagnet
• Magnetism and superconductivity of strongly correlated electrons on the triangular lattice
• Spin dynamics of the quasi two dimensional spin-1/2 quantum magnet Cs_2CuCl_4
• Spin Structure Factor of the Frustrated Quantum Magnet Cs_2CuCl_4

Cited by in corpus (7)

• Numerical Linked-Cluster Algorithms. I. Spin systems on square, triangular, and kagome lattices
• Algebraic vortex liquid theory of a quantum antiferromagnet on the kagome lattice
• Thermodynamics of the Up-Up-Down Phase of the S = 1/2 Triangular-Lattice Antiferromagnet Cs${}_2$CuBr${}_4$
• Magnetic order in coupled spin-half and spin-one Heisenberg chains in anisotropic triangular-lattice geometry
• Raman scattering in a Heisenberg {\boldmath $S=1/2$} antiferromagnet on the triangular lattice
• Excitation spectra and ground state properties of the layered spin-1/2 frustrated antiferromagnets Cs_2CuCl_4 and Cs_2CuBr_4
• Collective excitations in two-dimensional antiferromagnet in strong magnetic field