Quantum spin systems are representative of strongly interacting quantum many-body systems. ESR theories for these systems require careful treatment of microscopic interactions between electron spins. In this article, we review several ESR theories in low-dimensional quantum spin systems by giving our particular attention to the detection of hidden magnetic modes that are found or would be found thanks to some advantages of the ESR spectroscopy. We discuss an ESR caused by an interplay of a nonmagnetic impurity and magnetic excitations (Sect. 2), gapped modes with nonlinear field dependence in spin ladders (Sect. 3), and a quadrupolar mode that characterizes a hidden magnetic order called a spin-nematic order (Sect. 4).

中文翻译：

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奇异量子自旋系统中隐藏磁模式的 ESR 理论

量子自旋系统是强相互作用量子多体系统的代表。这些系统的 ESR 理论需要仔细处理电子自旋之间的微观相互作用。在本文中，我们通过特别关注发现或将要发现的隐藏磁模式的检测，回顾了低维量子自旋系统中的几种 ESR 理论，这要归功于 ESR 光谱的一些优势。我们讨论了由非磁性杂质和磁激发相互作用引起的 ESR（第 2 节）、自旋梯中具有非线性场依赖性的带隙模式（第 3 节）以及表征称为自旋的隐藏磁序的四极模式。向列顺序（第 4 节）。