Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4
Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4
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DOI：
10.1103/physrevx.8.031001
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发表时间：
2017-08
影响因子：
12.5
通讯作者：
F. Mahmood;Xinshu Zhang;Marcus Daum;Z. Dun;J. Paddison;N. Laurita;T. Hong;Haidong Zhou;P. Armitag
中科院分区：
文献类型：
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作者：
F. Mahmood;Xinshu Zhang;Marcus Daum;Z. Dun;J. Paddison;N. Laurita;T. Hong;Haidong Zhou;P. Armitag
自旋为1/2的三角形晶格反铁磁体YbMgGaO作为一种量子自旋-液体候选体，由于可能存在由自旋-轨道耦合引起的非对角各向异性交换作用，最近引起了人们的关注。量子自旋液体是否稳定取决于化合物的层状结构所固有的化学无序与各种交换作用的相互作用。为了更好地了解YbMgGaO的交换作用，我们将场偏振态下的时间域太赫兹光谱和非弹性中子散射测量相结合。太赫兹光谱学以这种方式起到高场电子自旋共振的作用，探测布里渊区中心的自旋波激发，理想地补充了中子散射。通过对太赫兹谱线宽度的分析，在4T以上的场下，符合我们所有光谱数据的全局自旋波对$g因子和交换相互作用产生了严格的限制。我们的结果表明YbMgGaO${4}$是一个容易平面的XXZ反铁磁体，它同时存在次导次近邻和弱各向异性非对角近邻相互作用。此外，所获得的$g$因子与以前的报告有很大不同。这项工作仅从高场数据就建立了YbMgGaO${4}$中交换相互作用的层次结构，从而强烈地约束了导致所观察到的自旋-液体现象的可能机制。
The spin-1/2 triangular lattice antiferromagnet YbMgGaO$_{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.