近日，德国路德维希马克西米利安大学Dmitri K. Efetov团队研究了魔角扭曲双层石墨烯中轻电子带和重电子带的相互作用。2025年5月22日出版的《自然—物理学》杂志发表了这项成果。

最近的研究表明，魔角扭曲双层石墨烯的强相关平带可能含有共存的轻载流子和重载流子。尽管输运和光谱测量暗示了这种行为，但尚未报道非相干重载流子的明显特征。研究组通过在栅极定义的p-n结中使用光热电效应对魔角扭曲双层石墨烯进行热电输运测量来提供证据。 

在低温下，研究组观察到莫尔超晶格非零整数填充处塞贝克系数的保符号、填充依赖振荡。这表明，即使费米能级通过相关态的电荷中性点进行调谐，一种载流子类型也占主导地位。在更高的温度下，热电响应提供了无序正常状态下强电子相关性的证据。该观测结果可以用对称破缺基态费米能级附近的轻、长寿命电子态和重、短命空穴激发之间的相互作用来解释。这些发现与拓扑重费米子模型在定性上是一致的。

附：英文原文

Title: Interplay between light and heavy electron bands in magic-angle twisted bilayer graphene

Author: Merino, Rafael Luque, Clugru, Dumitru, Hu, Haoyu, Dez-Mrida, Jaime, Dez-Carln, Andrs, Taniguchi, Takashi, Watanabe, Kenji, Seifert, Paul, Bernevig, B. Andrei, Efetov, Dmitri K.

Issue&Volume: 2025-05-22

Abstract: Recent studies have suggested that the strongly correlated flat bands of magic-angle twisted bilayer graphene may host coexisting light and heavy carriers. Although transport and spectroscopic measurements have hinted at this behaviour, distinct signatures of incoherent heavy carriers have not been reported. Here we provide evidence of this by performing thermoelectric transport measurements of magic-angle twisted bilayer graphene using the photo-thermoelectric effect in gate-defined p–n junctions. At low temperatures, we observe sign-preserving, filling-dependent oscillations of the Seebeck coefficient at non-zero integer fillings of the moiré superlattice. This suggests the preponderance of one carrier type even when the Fermi level is tuned through the charge neutrality point of the correlated states. At higher temperatures, the thermoelectric response provides evidence of strong electron correlations in the unordered, normal state. Our observations are explained by the interplay between light, long-lived electron states and heavy, short-lived hole excitations near the Fermi level of the symmetry-broken ground states. These findings are in qualitative agreement with the topological heavy fermion model.

DOI: 10.1038/s41567-025-02912-x

Source: https://www.nature.com/articles/s41567-025-02912-x