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arXiv · 2303.14903

Strong Inter-valley Electron-Phonon Coupling in Magic-Angle Twisted Bilayer Graphene

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

The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked enormous 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, utilizing angle-resolved photoemission spectroscopy with micrometer spatial resolution, we have revealed flat band replicas in superconducting MATBG, where MATBG is unaligned with its hexagonal boron nitride (hBN) substrate11. These replicas exhibit uniform energy spacing, approximately 150 +- 15 meV 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 hBN 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 inter-valley scattering. These findings, although do not necessarily put electron phonon coupling as the main driving force for the superconductivity in MATBG, unravel the unique electronic structure inherent in superconducting MATBG, thereby providing crucial information for understanding the unusual electronic landscape from which the superconductivity is derived.

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Cheng Chen, Kevin P. Nuckolls, Shuhan Ding, Wangqian Miao, Dillon Wong, Myungchul Oh, Ryan L. Lee, Shanmei He, Cheng Peng, Ding Pei, Yiwei Li, Chenyue Hao, Haoran Yan, Hanbo Xiao, Han Gao, Qiao Li, Shihao Zhang, Jianpeng Liu, Lin He, Kenji Watanabe, Takashi Taniguchi, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, Chu Li, Xu Han, Ding Pan, Zhongkai Liu, Xi Dai, Chaoxing Liu, B. Andrei Bernevig, Yao Wang, Ali Yazdani, Yulin Chen. 2023-03-27. Strong Inter-valley Electron-Phonon Coupling in Magic-Angle Twisted Bilayer Graphene. https://doi.org/10.1038/s41586-024-08227-w

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