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

Journal Article · · Nature (London)
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  1. ShanghaiTech University (China); University of Oxford (United Kingdom)
  2. Massachusetts Institute of Technology (MIT), Cambridge, MA (United States); Princeton University, NJ (United States)
  3. Emory University, Atlanta, GA (United States)
  4. University of California, Santa Barbara, CA (United States)
  5. Princeton University, NJ (United States)
  6. Pohang University of Science and Technology (POSTECH) (Korea, Republic of); Princeton University, NJ (United States)
  7. University of Oxford (United Kingdom)
  8. ShanghaiTech University (China)
  9. Wuhan University (China)
  10. Beijing Normal University (China)
  11. National Institute for Materials Science, Tsukuba (Japan)
  12. Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
  13. Hong Kong University of Science and Technology (China)
  14. Pennsylvania State University, University Park, PA (United States)
  15. Princeton University, NJ (United States); Donostia International Physics Center (Spain); IKERBASQUE, Basque Foundation for Science, Bilbao (Spain)
  16. Emory University, Atlanta, GA (United States); Clemson University, SC (United States)
+ Show Author Affiliations

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 ± 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.

Research Organization:
Princeton University, NJ (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); National Key R&D program of China; Shanghai Municipal Science and Technology Major Project; Gordon and Betty Moore Foundation’s EPiQS initiative; ARO MURI; ONR; National Science Foundation (NSF); Simons Investigator Grant; European Research Council (ERC); National Natural Science Foundation of China; Research Grants Council of the Hong Kong Special Administrative Region, China
Grant/Contract Number:
SC0016239; AC02-05CH11231; SC0024524; FG02-07ER46419
OSTI ID:
2499452
Alternate ID(s):
OSTI ID: 2569594
OSTI ID: 2571648
Journal Information:
Nature (London), Journal Name: Nature (London) Journal Issue: 8042 Vol. 636; ISSN 1476-4687; ISSN 0028-0836
Publisher:
Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
English

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