Searching for heavy fermion (HF) states in non-f-electron systems becomes an interesting issue, especially in the presence of magnetism, and can help explain the physics of complex compounds. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy, physical properties measurements, and the first-principles calculations, we observe the HF state in a 3d-electron van der Waals ferromagnet, Fe₃GeTe₂. Upon entering the ferromagnetic state, a massive spectral weight transfer occurs, which results from the exchange splitting. Meanwhile, the Fermi surface volume and effective electron mass are both enhanced. When the temperature drops below a characteristic temperature T*, heavy electrons gradually emerge with further enhanced effective electron mass. The coexistence of ferromagnetism and HF state can be well interpreted by the dual properties (itinerant and localized) of 3d electrons. This work expands the limit of ferromagnetic HF materials from f- to d-electron systems and illustrates the positive correlation between ferromagnetism and HF state in the 3d-electron material, which is quite different from the f-electron systems.

中文翻译：

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范德华流动铁磁体Fe3GeTe2中近藤晶格行为的出现。

在非f电子系统中寻找重费米子（HF）态成为一个有趣的问题，尤其是在存在磁性的情况下，它可以帮助解释复杂化合物的物理性质。使用角分辨光发射光谱，扫描隧道显微镜，物理性质测量和第一性原理计算，我们在3d电子范德华铁磁体Fe ₃ GeTe _2中观察到了HF状态。进入铁磁状态后，会发生大量的光谱权重转移，这是由交换分裂引起的。同时，费米表面体积和有效电子质量均提高。当温度降至特征温度T以下时*，随着有效电子质量的进一步提高，重电子逐渐出现。铁磁性和HF状态的共存可以通过3d电子的双重性质（流动和局部）很好地解释。这项工作将铁磁HF材料的极限从f电子系统扩展到d电子系统，并说明了3d电子材料中铁磁性与HF状态之间的正相关关系，这与f电子系统大不相同。