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The emergence of flat bands and correlated behaviors in “magic angle” twisted bilayer graphene (tBLG) has sparked tremendous interest, though many aspects of the system are under intense debate. Here we report transport properties of a tBLG device that has a twist angle of ~0.93º and a moiré superlattice period of ~15 nm. Though the angle is smaller than the magic angle by 15%, the device displays both the Mott-like insulator at half filling and, at slightly larger doping, superconductivity with a critical temperature ~0.35 K. At an electron concentration of ±5 electrons/moiré unit cell, we observe a narrow resistance peak with varying temperature that results from an energy gap ~0.1 meV, indicating the existence of an additional correlated insulating state. This is consistent with theory predicting the presence of a high-energy band with an energetically flat dispersion. The Landau fans emanating from this state has degeneracy 10±2, indicating novel spin-valley ordering. At a doping of ±12 electrons/moiré unit cell we observe a resistance peak due to the presence of Dirac points in the spectrum. Our results reveal that the "magic" range of tBLG is in fact larger than what is commonly expected based on the current knowledge, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG.

権利情報:

• Creative Commons BY-NC Attribution-NonCommercial 4.0 International
  

キーワード: Twisted bilayer graphene, superconductivity, Mott-like insulating state

刊行年月日: 2019-09-06

出版者: American Association for the Advancement of Science (AAAS)

掲載誌:

• Science Advances (ISSN: 23752548) vol. 5 issue. 9

研究助成金:

• MEXT Elemental Strategy Initiative
• National Science Foundation DMR 1420451
• U.S. Department of Energy 46940-DE-SC0010597
• Army Research Office W911NF-18-1-0416

原稿種別: 出版者版 (Version of record)

MDR DOI:

公開URL: https://doi.org/10.1126/sciadv.aaw9770

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更新時刻: 2025-02-23 22:50:59 +0900

MDRでの公開時刻: 2025-02-23 22:51:00 +0900