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

The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked considerable research interest 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 – 13 . However, despite the dedication of intensive experimental efforts and the proposal of several possible pairi...

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Published in:Nature (London) Vol. 636; no. 8042; pp. 342 - 347
Main Authors: 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
Format: Journal Article
Language:English
Published: London Nature Publishing Group UK 12.12.2024
Nature Publishing Group
Subjects:
140/146
639/301/357/918/1052
639/766/119/1003
639/766/119/995
CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
Electronic properties and devices
Electronic properties and materials
Humanities and Social Sciences
multidisciplinary
Science
Science (multidisciplinary)
Superconducting properties and materials
ISSN:0028-0836, 1476-4687, 1476-4687
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Summary:The unusual properties of superconductivity in magic-angle twisted bilayer graphene (MATBG) have sparked considerable research interest 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 – 13 . However, despite the dedication of intensive experimental efforts and the proposal of several possible pairing mechanisms 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 – 24 , 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 11 . These replicas show 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 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. Angle-resolved photoemission spectroscopy of superconducting magic-angle twisted bilayer graphene reveals flat-band replicas that are indicative of strong electron–phonon coupling; these replicas are absent in non-superconducting twisted bilayer graphene.
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Shanghai Municipal Science and Technology Major Project
ARO MURI
Research Grants Council of the Hong Kong Special Administrative Region, China
ONR
Simons Investigator Grant
USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
SC0016239; AC02-05CH11231; SC0024524; FG02-07ER46419
National Natural Science Foundation of China
National Science Foundation (NSF)
European Research Council (ERC)
National Key R&D program of China
Gordon and Betty Moore Foundation’s EPiQS initiative
ISSN:0028-0836
1476-4687
1476-4687
DOI:10.1038/s41586-024-08227-w