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arXiv · 2602.14563

Magnetic excitations in the Kitaev material Na$_2$IrO$_3$ studied by neutron scattering

Alexandre Bertin·Hengdi Zhao·Gang Cao·Andrea Piovano·Paul Steffens·Alexandre Ivanov·Markus Braden
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Abstract

Inelastic neutron scattering experiments with a large set of comounted Na$_2$IrO$_3$ crystals reveal the low-energy magnon dispersion in this candidate material for Kitaev physics. The magnon gap amounts to 1.7(1) meV and can be interpreted similarly to the sister compound $\alpha$-RuCl$_{3}$ to stem from the zone boundaries in the antiferromagnetic zigzag structure. The neutron experiments find no evidence for low-energy excitations with ferromagnetic character, which contrasts to the findings in $\alpha$-RuCl$_{3}$. Our results are consistent with a recently proposed microscopic model that involves an antiferromagnetic Heisenberg nearest-neighbor exchange in Na$_2$IrO$_3$ in contrast to the ferromagnetic one considered for $\alpha$-RuCl$_{3}$. Although the magnetic response shows the signatures of bond-directional anisotropy in both materials the different relative signs of Kitaev and Heisenberg interaction result in different deviations from the initial Kitaev model. Low-energy ferromagnetic fluctuations cannot be considered as a fingerprint of ferromagnetic Kitaev interaction.

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Alexandre Bertin, Hengdi Zhao, Gang Cao, Andrea Piovano, Paul Steffens, Alexandre Ivanov, Markus Braden. 2026-02-16. Magnetic excitations in the Kitaev material Na$_2$IrO$_3$ studied by neutron scattering. https://doi.org/10.1103/mvn9-nj5n

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