Kitaev interactions underlying a quantum spin liquid have been long sought, but experimental data from which their strengths can be determined directly is still lacking. Here, by carrying out inelastic neutron scattering measurements on high-quality single crystals of α-RuCl3, we observe spin-wave spectra with a gap of ∼2 meV around the M point of the two-dimensional Brillouin zone. We derive an effective-spin model in the strong-coupling limit based on energy bands obtained from first-principle calculations, and find that the anisotropic Kitaev interaction K term and the isotropic antiferromagentic off-diagonal exchange interaction Γ term are significantly larger than the Heisenberg exchange coupling J term. Our experimental data can be well fit using an effective-spin model with K=−6.8 meV and Γ=9.5 meV. These results demonstrate explicitly that Kitaev physics is realized in real materials.
@article{arxiv.1702.04920,
title = {Spin-wave excitations evidencing the Kitaev interaction in single crystalline $\alpha$-RuCl$_3$},
author = {Kejing Ran and Jinghui Wang and Wei Wang and Zhao-Yang Dong and Xiao Ren and Song Bao and Shichao Li and Zhen Ma and Yuan Gan and Youtian Zhang and J. T. Park and Guochu Deng and S. Danilkin and Shun-Li Yu and Jian-Xin Li and Jinsheng Wen},
journal= {arXiv preprint arXiv:1702.04920},
year = {2017}
}