Unambiguous identification of fractionalized excitations in quantum spin liquids has been a long-standing issue in correlated topological phases. Conventional spectroscopic probes, such as the dynamical spin structure factor, can only detect composites of fractionalized excitations, leading to a broad continuum in energy. Lacking a clear signature in conventional probes has been the biggest obstacle in the field. In this work, we theoretically investigate what kinds of distinctive signatures of fractionalized excitations can be probed in two-dimensional nonlinear spectroscopy by considering the exactly solvable Kitaev spin liquids. We demonstrate the existence of a number of salient features of the Majorana fermions and fluxes in two-dimensional nonlinear spectroscopy, which provide crucial information about such excitations.

中文翻译：

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Kitaev自旋液体的二维非线性光谱理论

量子自旋液体中分数激发的明确识别在相关拓扑阶段一直是一个长期存在的问题。常规的光谱探针（例如动态自旋结构因子）只能检测分数激发的复合物，从而产生广泛的能量连续体。在常规探针中缺乏清晰的特征一直是该领域中的最大障碍。在这项工作中，我们在理论上通过考虑可完全溶解的Kitaev自旋液体，研究了在二维非线性光谱学中可以探测出哪种类型的分步激发特征。我们证明了二维非线性光谱学中马约拉纳费米子和通量的许多显着特征的存在，这些特征提供了有关此类激发的关键信息。