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arXiv · 1306.4678

Fractional spinon excitations in the quantum Heisenberg antiferromagnetic chain

M. Mourigal·M. Enderle·A. Klöpperpieper·J. -S. Caux·A. Stunault·H. M. Rønnow
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Abstract

Assemblies of interacting quantum particles often surprise us with properties that are difficult to predict. One of the simplest quantum many-body systems is the spin 1/2 Heisenberg antiferromagnetic chain, a linear array of interacting magnetic moments. Its exact ground state is a macroscopic singlet entangling all spins in the chain. Its elementary excitations, called spinons, are fractional spin 1/2 quasiparticles; they are created and detected in pairs by neutron scattering. Theoretical predictions show that two-spinon states exhaust only 71% of the spectral weight while higher-order spinon states, yet to be experimentally located, are predicted to participate in the remaining. Here, by accurate absolute normalization of our inelastic neutron scattering data on a compound realizing the model, we account for the full spectral weight to within 99(8)%. Our data thus establish and quantify the existence of higher-order spinon states. The observation that within error bars, the entire weight is confined within the boundaries of the two-spinon continuum, and that the lineshape resembles a rescaled two-spinon one, allow us to develop a simple physical picture for understanding multi-spinon excitations.

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M. Mourigal, M. Enderle, A. Klöpperpieper, J. -S. Caux, A. Stunault, H. M. Rønnow. 2013-06-19. Fractional spinon excitations in the quantum Heisenberg antiferromagnetic chain. https://doi.org/10.1038/nphys2652

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