二维铁磁绝缘体中临界涨落的磁共振研究
Abnormal Critical Fluctuations Revealed by Magnetic Resonance in the Two-Dimensional Ferromagnetic Insulators
摘要：
相变和临界现象是一个充满物理范式和意外发现的领域，它们受涨落和关联的支配。特别是对于二维磁性，金兹伯格准则的限制导致了在临界点附近打破平均场论的增强的波动。本文利用磁共振研究了二维铁磁绝缘体$\rm CrXTe_3 (X=Si, Ge)$中的临界涨落行为。在推导出经典和量子磁共振模型后，我们认为所测得的$g$因子的显著各向异性位移源于各向异性相互作用的波动。涨落背后的$g$因子的推导与纯自旋态一致（$\rm CrSiTe_3$的${g\approx}$为2.050（10），$\rm CrGeTe_3$为2.039（10））。此外，$g$位移的异常增强，辅以比热和磁力测量，表明$\rm CrSiTe_3$表现出比$\rm CrGeTe_3$更典型的二维性质，可能更接近量子临界点。
英文摘要：
Phase transitions and critical phenomena, which are dominated by fluctuations and correlations, are one of the fields replete with physical paradigms and unexpected discoveries. Especially for two-dimensional magnetism, the limitation of the Ginzburg criterion leads to enhanced fluctuations breaking down the mean-field theory near a critical point. Here, by means of magnetic resonance, we investigate the behavior of critical fluctuations in the two-dimensional ferromagnetic insulators $\rm CrXTe_3 (X=Si, Ge)$. After deriving the classical and quantum models of magnetic resonance, we deem the dramatic anisotropic shift of the measured $g$ factor to originate from fluctuations with anisotropic interactions. The deduction of the $g$ factor behind the fluctuations is consistent with the spin-only state (${g\approx}$ 2.050(10) for $\rm CrSiTe_3$ and 2.039(10) for $\rm CrGeTe_3$). Furthermore, the abnormal enhancement of $g$ shift, supplemented by specific heat and magnetometry measurements, suggests that $\rm CrSiTe_3$ exhibits a more typical two-dimensional nature than $\rm CrGeTe_3$ and may be closer to the quantum critical point.
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