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arXiv · 1503.07593

Spin-orbit excitations and electronic structure of the putative Kitaev magnet $\alpha$-RuCl$_3$

Luke J. Sandilands·Yao Tian·Anjan A. Reijnders·Heung-Sik Kim·Kemp W. Plumb·Hae-Young Kee·Young-June Kim·Kenneth S. Burch
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Abstract

Mott insulators with strong spin-orbit coupling have been proposed to host unconventional magnetic states, including the Kitaev quantum spin liquid. The 4$d$ system $\alpha$-RuCl$_3$ has recently come into view as a candidate Kitaev system, with evidence for unusual spin excitations in magnetic scattering experiments. We apply a combination of optical spectroscopy and Raman scattering to study the electronic structure of this material. Our measurements reveal a series of orbital excitations involving localized total angular momentum states of the Ru ion, implying that strong spin-orbit coupling and electron-electron interactions coexist in this material. Analysis of these features allows us to estimate the spin-orbit coupling strength, as well as other parameters describing the local electronic structure, revealing a well-defined hierarchy of energy scales within the Ru $d$ states. By comparing our experimental results with density functional theory calculations, we also clarify the overall features of the optical response. Our results demonstrate that $\alpha$-RuCl$_3$ is an ideal material system to study spin-orbit coupled magnetism on the honeycomb lattice.

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Luke J. Sandilands, Yao Tian, Anjan A. Reijnders, Heung-Sik Kim, Kemp W. Plumb, Hae-Young Kee, Young-June Kim, Kenneth S. Burch. 2015-03-26. Spin-orbit excitations and electronic structure of the putative Kitaev magnet $\alpha$-RuCl$_3$. https://doi.org/10.1103/physrevb.93.075144

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