Longitudinal excitations in quantum antiferromagnets

Abstract

By extending our recently proposed magnon-density-waves to low dimensions, we investigate, using a microscopic many-body approach, the longitudinal excitations of the quasi-one-dimensional (quasi-1d) and quasi-2d Heisenberg antiferromagnetic systems on a bipartite lattice with a general spin quantum number. We obtain the full energy spectrum of the longitudinal mode as a function of the coupling constants in the original lattice Hamiltonian and find that it always has a non-zero energy gap if the ground state has a long-range order and becomes gapless for the pure isotropic 1d model. The numerical value of the minimum gap in our approximation agrees with that of a longitudinal mode observed in the quasi-1d antiferromagnetic compound KCuF${}_3$ at low temperature. It will be interesting to compare values of the energy spectrum at other momenta if their experimental results are available.

19 pages, 4 figures

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Cited by in corpus (5)

• Amplitude mode in the planar triangular antiferromagnet Na${}_{0.9}$MnO${}_2$
• Longitudinal Excitations in Bipartite and Hexagonal Antiferromagnetic Spin Lattices
• Excited states of the quasi-one-dimensional hexagonal quantum antiferromagnets
• Longitudinal excitations in triangular lattice antiferromagnets
• The effects of three magnons interactions in the magnon-density waves of triangular spin lattices