近日，西班牙巴塞罗那科学技术学院Frank H. L. Koppens团队研究了对称扭曲三层石墨烯的光电显微镜分析。这一研究成果于2025年11月20日发表在《自然—物理学》杂志上。

目前尚未能对魔角扭转双层石墨烯平带中出现的关联绝缘体与超导现象完成完整的微观描述。电子输运与扫描隧道显微实验提示了局域化与扩展电子轨道之间的二分性，但关于这两类载流子共存的明确证据仍有待发掘。

研究组通过对称性扭转三层石墨烯平带中的局域光热电测量，观测到平带整数填充附近塞贝克系数的振荡现象，这标志着电子关联效应的存在，同时伴随着莫特公式预测的失效。测量结果显示塞贝克系数呈现整体负偏移，且莫尔超晶格所有正整数填充处均出现局域光电压峰值。这进一步表明其偏离了经典双带半导体塞贝克响应规律。该发现可用莫尔石墨烯拓扑平带中的重费米子模型进行解释，也为应用局域热电测量技术研究其他强关联材料开辟了途径。

附：英文原文

Title: Photovoltage microscopy of symmetrically twisted trilayer graphene

Author: Batlle Porro, Sergi, Clugru, Dumitru, Hu, Haoyu, Krishna Kumar, Roshan, Hesp, Niels C. H., Watanabe, Kenji, Taniguchi, Takashi, Bernevig, B. Andrei, Stepanov, Petr, Koppens, Frank H. L.

Issue&Volume: 2025-11-20

Abstract: A full microscopic description of the correlated insulators and superconductivity that occur in the flat bands of magic angle twisted bilayer graphene has not yet been found. Electronic transport and scanning tunnelling microscopy experiments have suggested a dichotomy between local and extended electronic orbitals, but definitive evidence for the coexistence of these two carrier types is still sought after. Here we report local photothermoelectric measurements in the flat electronic bands of symmetrically twisted trilayer graphene. We observe oscillations of the Seebeck coefficient around integer fillings of the flat band, signalling the presence of electron correlations, coupled with a breakdown of the predictions of the Mott formula. Our measurements reveal an overall negative offset of the Seebeck coefficient and peaks of the local photovoltage values at all positive integer fillings of the moiré superlattice. This further indicates a deviation from the classical two-band semiconductor Seebeck response. Our findings may be interpreted using the heavy-fermion model in the topological flat bands of moiré graphene and highlight an avenue to apply local thermoelectric measurements to other strongly correlated materials.

DOI: 10.1038/s41567-025-03071-9

Source: https://www.nature.com/articles/s41567-025-03071-9