Triangular lattice of rare-earth ions with interacting effective spin-$1/2$ local moments is an ideal platform to explore the physics of quantum spin liquids (QSLs) in the presence of strong spin-orbit coupling, crystal electric fields, and geometrical frustration. The Yb delafossites, $\mathrm{NaYb}C{h}_2$ ($Ch=\mathrm{O}$, S, Se) with Yb ions forming a perfect triangular lattice, have been suggested to be candidates for QSLs. Previous thermodynamics, nuclear magnetic resonance, and powder-sample neutron scattering measurements on ${\mathrm{NaYbCh}}_2$ have supported the suggestion of the QSL ground states. The key signature of a QSL, the spin excitation continuum, arising from the spin quantum number fractionalization, has not been observed. Here we perform both elastic and inelastic neutron scattering measurements as well as detailed thermodynamic measurements on high-quality single-crystal ${\mathrm{NaYbSe}}_2$ samples to confirm the absence of long-range magnetic order down to 40 mK, and further reveal a clear signature of magnetic excitation continuum extending from 0.1 to 2.5 meV. The comparison between the structure of the magnetic excitation spectra and the theoretical expectation from the spinon continuum suggests that the ground state of ${\mathrm{NaYbSe}}_2$ is a QSL with a spinon Fermi surface.

中文翻译：

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三角晶格反铁磁体NaYbSe2中的自旋费米表面自旋液体

稀土离子的三角形晶格具有有效的自旋相互作用$\mathrm{1个}/\mathrm{2个}$在存在强自旋轨道耦合，晶体电场和几何受挫的情况下，局部矩是探索量子自旋液体（QSL）物理学的理想平台。Yb delafossites，$钠C{H}_{\mathrm{2个}}$ （$CH=\mathrm{Ø}$，S，Se），Yb离子形成一个完美的三角晶格，已被建议作为QSL的候选者。以前的热力学，核磁共振和粉末样品中子散射测量${钠}_{\mathrm{2个}}$支持QSL基本状态的建议。还没有观察到QSL的关键特征，即自旋量子数分级化产生的自旋激发连续体。在这里，我们对高品质单晶进行弹性和非弹性中子散射测量以及详细的热力学测量。${\mathrm{硒化钠}}_{\mathrm{2个}}$样品以确认不存在低至40 mK的远距离磁阶，并进一步揭示了从0.1到2.5 meV延伸的连续磁激发的清晰特征。磁激发光谱的结构与自旋连续体的理论期望的比较表明，原子的基态。${\mathrm{硒化钠}}_{\mathrm{2个}}$ 是具有自旋费米表面的QSL。