近日，上海科技大学的陈宇林与美国埃默里大学的Yao Wang等人合作并取得一项新进展。他们实现了魔角扭曲双层石墨烯中的强电子-声子耦合。相关研究成果已于2024年12月11日在国际权威学术期刊《自然》上发表。

据悉，魔角扭曲双层石墨烯（MATBG）中超导性的独特性质已引起了广泛的研究兴趣。然而，尽管人们投入了大量的实验努力，并提出了几种可能的配对机制，但其超导性的起源仍然是个谜。

该研究团队利用具有微米空间分辨率的角度分辨光发射光谱技术，在超导的魔角扭曲双层石墨烯（MATBG）中发现了平带复制带，此时MATBG与其六方氮化硼衬底未对齐。这些复制带显示出均匀的能量间隔，大约相隔150±15毫电子伏特，表明存在强烈的电子-玻色子耦合。

引人注目的是，在非超导的扭曲双层石墨烯（TBG）系统中，无论是MATBG与六方氮化硼对齐时，还是TBG偏离魔角时，这些复制带都不存在。计算结果表明，超导MATBG中平带复制带的形成归因于，平带电子与石墨烯K点处的光学声子模式之间的强耦合，这种耦合是通过谷间散射实现的。

这些发现虽然并不一定将电子-声子耦合视为MATBG超导性的主要驱动力，但揭示了超导MATBG中固有的电子结构，从而为理解其超导性所源自的反常电子态提供了关键信息。

附：英文原文

Title: Strong electron–phonon coupling in magic-angle twisted bilayer graphene

Author: Chen, Cheng, Nuckolls, Kevin P., Ding, Shuhan, Miao, Wangqian, Wong, Dillon, Oh, Myungchul, Lee, Ryan L., He, Shanmei, Peng, Cheng, Pei, Ding, Li, Yiwei, Hao, Chenyue, Yan, Haoran, Xiao, Hanbo, Gao, Han, Li, Qiao, Zhang, Shihao, Liu, Jianpeng, He, Lin, Watanabe, Kenji, Taniguchi, Takashi, Jozwiak, Chris, Bostwick, Aaron, Rotenberg, Eli, Li, Chu, Han, Xu, Pan, Ding, Liu, Zhongkai, Dai, Xi, Liu, Chaoxing, Bernevig, B. Andrei, Wang, Yao, Yazdani, Ali, Chen, Yulin

Issue&Volume: 2024-12-11

Abstract: The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked considerable research interest. However, despite the dedication of intensive experimental efforts and the proposal of several possible pairing mechanisms, the origin of its superconductivity remains elusive. Here, by utilizing angle-resolved photoemission spectroscopy with micrometre spatial resolution, we reveal flat-band replicas in superconducting MATBG, where MATBG is unaligned with its hexagonal boron nitride substrate. These replicas show uniform energy spacing, approximately 150±15meV apart, indicative of strong electron–boson coupling. Strikingly, these replicas are absent in non-superconducting twisted bilayer graphene (TBG) systems, either when MATBG is aligned to hexagonal boron nitride or when TBG deviates from the magic angle. Calculations suggest that the formation of these flat-band replicas in superconducting MATBG are attributed to the strong coupling between flat-band electrons and an optical phonon mode at the graphene K point, facilitated by intervalley scattering. These findings, although they do not necessarily put electron–phonon coupling as the main driving force for the superconductivity in MATBG, unravel the electronic structure inherent in superconducting MATBG, thereby providing crucial information for understanding the unusual electronic landscape from which its superconductivity is derived.

DOI: 10.1038/s41586-024-08227-w

Source: https://www.nature.com/articles/s41586-024-08227-w