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arXiv · 1708.07503

Hierarchy of exchange interactions in the triangular-lattice spin-liquid YbMgGaO$_{4}$

Xinshu Zhang·Fahad Mahmood·Marcus Daum·Zhiling Dun·Joseph A. M. Paddison·Nicholas J. Laurita·Tao Hong·Haidong Zhou·N. P. Armitage·Martin Mourigal
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Abstract

The spin-1/2 triangular lattice antiferromagnet YbMgGaO$_{4}$ has attracted recent attention as a quantum spin-liquid candidate with the possible presence of off-diagonal anisotropic exchange interactions induced by spin-orbit coupling. Whether a quantum spin-liquid is stabilized or not depends on the interplay of various exchange interactions with chemical disorder that is inherent to the layered structure of the compound. We combine time-domain terahertz spectroscopy and inelastic neutron scattering measurements in the field polarized state of YbMgGaO$_{4}$ to obtain better microscopic insights on its exchange interactions. Terahertz spectroscopy in this fashion functions as high-field electron spin resonance and probes the spin-wave excitations at the Brillouin zone center, ideally complementing neutron scattering. A global spin-wave fit to all our spectroscopic data at fields over 4T, informed by the analysis of the terahertz spectroscopy linewidths, yields stringent constraints on $g$-factors and exchange interactions. Our results paint YbMgGaO$_{4}$ as an easy-plane XXZ antiferromagnet with the combined and necessary presence of sub-leading next-nearest neighbor and weak anisotropic off-diagonal nearest-neighbor interactions. Moreover, the obtained $g$-factors are substantially different from previous reports. This works establishes the hierarchy of exchange interactions in YbMgGaO$_{4}$ from high-field data alone and thus strongly constrains possible mechanisms responsible for the observed spin-liquid phenomenology.

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Xinshu Zhang, Fahad Mahmood, Marcus Daum, Zhiling Dun, Joseph A. M. Paddison, Nicholas J. Laurita, Tao Hong, Haidong Zhou, N. P. Armitage, Martin Mourigal. 2017-08-24. Hierarchy of exchange interactions in the triangular-lattice spin-liquid YbMgGaO$_{4}$. https://doi.org/10.1103/physrevx.8.031001

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