Significant efforts have focused on the magnetic excitations of relativistic Mott insulators, predicted to realize the Kitaev quantum spin liquid (QSL). This exactly solvable model involves a highly entangled state resulting from bond-dependent Ising interactions that produce excitations which are non-local in terms of spin flips. A key challenge in real materials is identifying the relative size of the non-Kitaev terms and their role in the emergence or suppression of fractional excitations. Here, we identify the energy and temperature boundaries of non-Kitaev interactions by direct comparison of the Raman susceptibility of α-RuCl₃ with quantum Monte Carlo (QMC) results for the Kitaev QSL. Moreover, we further confirm the fractional nature of the magnetic excitations, which is given by creating a pair of fermionic quasiparticles. Interestingly, this fermionic response remains valid in the non-Kitaev range. Our results and focus on the use of the Raman susceptibility provide a stringent new test for future theoretical and experimental studies of QSLs.

巨大的努力集中在相对论性Mott绝缘子的磁激发上，预计将实现Kitaev量子自旋液体（QSL）。这种完全可解的模型涉及一个高度纠缠的状态，该状态是由依赖于键的伊辛相互作用产生的，该相互作用产生的自旋翻转非局部激发。实际材料中的关键挑战是确定非Kitaev项的相对大小及其在分数激励的出现或抑制中的作用。在这里，我们通过直接比较α- RuCl ₃的拉曼磁化率来确定非Kitaev相互作用的能量和温度边界Kitaev QSL的量子蒙特卡罗（QMC）结果。此外，我们进一步确定了磁激发的分数性质，这是通过创建一对铁离子准粒子而给出的。有趣的是，这种铁离子反应在非Kitaev范围内仍然有效。我们的研究结果以及对拉曼磁化率的关注，为未来QSL的理论和实验研究提供了严格的新检验。