Slow convergence of spin-wave expansion and magnon dispersion in the 1/3 plateau of the triangular XXZ antiferromagnet

Abstract

Motivated by recent experiments on the quantum magnet K${}_2$Co(SeO${}_3$)${}_2$, we study theoretically the excitation spectrum of the nearest-neighbour triangular XXZ model in the limit of strong easy-axis anisotropy, within the up-up-down (1/3-plateau) phase. We make an expansion in $\alpha =J_{xy}/J_{zz}$ instead of $1/S$ and calculate the magnon dispersion for any value of the spin $S$ at second order in $\alpha$, with two important conclusions: (i) the 1/S expansion converges very slowly for S=1/2, making spin-wave theory quantitatively inaccurate up to very large orders; (ii) compared to the linear spin-wave predictions, our magnon dispersion presents a much better agreement with experimental results on K${}_2$Co(SeO${}_3$)${}_2$, for which $\alpha \simeq 0.08$.

6 pages, 3 figures

References in corpus (10)

• Strong quantum fluctuations in a quantum spin liquid candidate with a Co-based triangular lattice
• The phase diagram of the antiferromagnetic XXZ model on the triangular lattice
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• Variational wavefunction study of the triangular lattice supersolid
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Cited by in corpus (3)

• Emergent Spin Supersolids in Frustrated Quantum Materials
• Symmetry breaking and competing valence bond states in the star lattice Heisenberg antiferromagnet
• Canted ferromagnetic order in a distorted triangular-lattice magnet Na${}_2$SrCo(VO${}_4$)${}_2$