Fifty years after Anderson’s resonating valence-bond proposal, the spin-1/2 triangular-lattice Heisenberg antiferromagnet (TLHAF) remains the ultimate platform to explore highly entangled quantum spin states in proximity to magnetic order. Yb-based delafossites are ideal candidate TLHAF materials, which allow experimental access to the full range of applied in-plane magnetic fields. We perform a systematic neutron scattering study of CsYbSe₂, first proving the Heisenberg character of the interactions and quantifying the second-neighbor coupling. We then measure the complex evolution of the excitation spectrum, finding extensive continuum features near the 120°-ordered state, throughout the 1/3-magnetization plateau and beyond this up to saturation. We perform cylinder matrix-product-state (MPS) calculations to obtain an unbiased numerical benchmark for the TLHAF and spectacular agreement with the experimental spectra. The measured and calculated longitudinal spectral functions reflect the role of multi-magnon bound and scattering states. These results provide valuable insight into unconventional field-induced spin excitations in frustrated quantum materials.

在安德森提出共振价键提议 50 年后，自旋 1/2 三角晶格海森堡反铁磁体 (TLHAF) 仍然是探索接近磁序的高度纠缠量子自旋态的终极平台。镱基铜铁矿是理想的 TLHAF 材料候选材料，它允许实验获得全范围的应用面内磁场。_{我们对 CsYbSe 2}进行了系统的中子散射研究，首先证明相互作用的海森堡特征并量化二邻耦合。然后，我们测量激发光谱的复杂演化，发现在 120° 有序态附近、整个 1/3 磁化平台以及超过该平台直至饱和的广泛连续谱特征。我们执行柱面矩阵乘积状态 (MPS) 计算，以获得 TLHAF 的无偏数值基准，并与实验光谱高度一致。测量和计算的纵向光谱函数反映了多磁振子束缚态和散射态的作用。这些结果为受挫量子材料中非常规场诱导的自旋激发提供了有价值的见解。