近日，美国布朗大学J. I. A.Li课题组与桑迪亚国家实验室的Andrew Mounce等人合作并取得一项新进展，经过不懈努力，他们提出了狄拉克复原驱动了扭曲双层石墨烯的共振响应。相关研究成果已于2023年5月11日在国际知名学术期刊《自然—物理学》上发表。
该研究团队利用电阻探测电子自旋共振技术，在魔角附近扭曲双层石墨烯中观察到了低能集体激发。实验结果表明，微波共振的产生和探测依赖于平坦莫尔能带内的强相关性。具体而言，首先，共振响应的开始与莫尔半填充处的自发味极化相一致，但在同位旋未极化密度范围内不存在。其次，研究人员在各种没有平带的系统上进行了相同的测量，但观察到没有共振响应的迹象。他们认为，魔角附近的共振响应源于狄拉克复原和由此产生的同位旋序。
据悉，集体激发包含了关于强关联体系基态电子序的关键信息。最近的实验提到，在魔角石墨烯莫尔带的自旋和谷同位旋通道中存在多种集体模式。然而，由于缺乏自旋探针，无法直接观察这些集体激发。
附：英文原文
Title: Dirac revivals drive a resonance response in twisted bilayer graphene
Author: Morissette, Erin, Lin, Jiang-Xiazi, Sun, Dihao, Zhang, Liangji, Liu, Song, Rhodes, Daniel, Watanabe, Kenji, Taniguchi, Takashi, Hone, James, Pollanen, Johannes, Scheurer, Mathias S., Lilly, Michael, Mounce, Andrew, Li, J. I. A.
Issue&Volume: 2023-05-11
Abstract: Collective excitations contain key information regarding the electronic order of the ground state of strongly correlated systems. Various collective modes in the spin and valley isospin channels of magic-angle graphene moiré bands have been alluded to by a series of recent experiments. However, a direct observation of collective excitations has been impossible due to the lack of a spin probe. Here we observe low-energy collective excitations in twisted bilayer graphene near the magic angle, using a resistively detected electron spin resonance technique. Two independent observations show that the generation and detection of microwave resonance relies on the strong correlations within the flat moiré energy band. First, the onset of the resonance response coincides with the spontaneous flavour polarization at moiré half-filling, but is absent in the isospin unpolarized density range. Second, we perform the same measurement on various systems that do not have flat bands and observe no indication of a resonance response in these samples. Our explanation is that the resonance response near the magic angle originates from Dirac revivals and the resulting isospin order.
DOI: 10.1038/s41567-023-02060-0
Source: https://www.nature.com/articles/s41567-023-02060-0