A spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) is a prototypical frustrated quantum magnet, which exhibits remarkable quantum many-body effects that arise from the synergy between spin frustration and quantum fluctuation. The ground-state properties of a spin-1/2 TLHAF are theoretically well understood. However, the theoretical consensus regarding the magnetic excitations is limited. The experimental study of the magnetic excitations in spin-1/2 TLHAFs has also been limited. Here we show the structure of magnetic excitations in the spin-1/2 TLHAF Ba₃CoSb₂O₉ investigated by inelastic neutron scattering. Significantly different from theoretical expectations, the excitation spectrum has a three-stage energy structure. The lowest-energy first stage is composed of dispersion branches of single-magnon excitations. The second and third stages are dispersive continua accompanied by a columnar continuum extending above 10 meV, which is six times larger than the exchange interaction J = 1.67 meV. Our results indicate the shortcomings of the current theoretical framework.Two-dimensional frustrated magnets are heavily studied because theories predict that quantum effects may lead to the emergence of fractionalized excitations. Ito et al. use inelastic neutron scattering to show that the excitation spectrum of Ba₃CoSb₂O₉ disagrees with current theoretical expectations.

中文翻译：

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自旋1/2三角形格Heisenberg反铁磁体Ba3CoSb2O9中的磁激发结构。

自旋1/2三角形晶格海森堡反铁磁体（TLHAF）是典型的受挫量子磁体，其表现出显着的量子多体效应，这是由自旋受挫与量子涨落之间的协同作用引起的。理论上很好地了解了自旋1/2 TLHAF的基态性质。但是，关于磁激励的理论共识是有限的。自旋1/2 TLHAFs中的磁激发的实验研究也受到限制。在这里，我们显示了自旋1/2 TLHAF Ba ₃ CoSb ₂ O _9中的磁激发结构。通过非弹性中子散射进行研究。激发光谱具有三阶段的能量结构，与理论预期有很大不同。最低能量的第一级由单磁振子激发的色散分支组成。第二阶段和第三阶段是弥散连续性，伴随着一个柱状连续体，延伸至10 meV以上，是交换相互作用J = 1.67 meV的六倍。我们的研究结果表明了当前理论框架的不足。由于理论预言了量子效应可能导致分数激发的出现，因此对二维受阻磁体进行了深入研究。伊藤等。非弹性中子散射表明Ba ₃ CoSb ₂ O ₉的激发光谱 不符合当前的理论期望。