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Elementary Excitations of Heisenberg Ferrimagnetic Spin Chains

Shoji Yamamoto·S. Brehmer·H. -J. Mikeska
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Abstract

We numerically investigate elementary excitations of the Heisenberg alternating-spin chains with two kinds of spins 1 and 1/2 antiferromagnetically coupled to each other. Employing a recently developed efficient Monte Carlo technique as well as an exact diagonalization method, we verify the spin-wave argument that the model exhibits two distinct excitations from the ground state which are gapless and gapped. The gapless branch shows a quadratic dispersion in the small-momentum region, which is of ferromagnetic type. With the intention of elucidating the physical mechanism of both excitations, we make a perturbation approach from the decoupled-dimer limit. The gapless branch is directly related to spin 1's, while the gapped branch originates from cooperation of the two kinds of spins.

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Shoji Yamamoto, S. Brehmer, H. -J. Mikeska. 1997-10-30. Elementary Excitations of Heisenberg Ferrimagnetic Spin Chains. https://doi.org/10.1103/physrevb.57.13610

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