The direct electron paramagnetic resonance (EPR) absorption between the singlet ground state and the triplet excited states of spin gap systems is investigated. Such an absorption, which is forbidden by the conservation of the total spin quantum number in isotropic Hamiltonians, is allowed by some anisotropies; the staggered g-tensor and the Dzyaloshinskii–Moriya interaction. Selection rules in the presence of these interactions were presented in our previous works. We review the selection rules of the EPR transition of the spin gap with some numerical demonstrations and discuss some applications.

中文翻译：

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用于观察自旋间隙的选择规则的 EPR 理论

研究了自旋隙系统的单重基态和三重激发态之间的直接电子顺磁共振 (EPR) 吸收。这种吸收是由各向同性哈密顿量的总自旋量子数守恒所禁止的，而某些各向异性是允许的；交错的 g-张量和 Dzyaloshinskii-Moriya 相互作用。我们之前的作品中介绍了存在这些相互作用的选择规则。我们通过一些数值演示回顾了自旋间隙 EPR 跃迁的选择规则并讨论了一些应用。