Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle

Emilio Codecido; Qiyue Wang; Ryan Koester; Shi Che; Haidong Tian; Rui Lv; Son Tran; Kenji Watanabe; Takashi Taniguchi; Fan Zhang; Marc Bockrath; Chun Ning Lau

doi:10.1126/sciadv.aaw9770

Article Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle

Emilio Codecido ; Qiyue Wang ; Ryan Koester ; Shi Che ; Haidong Tian ; Rui Lv ; Son Tran ; Kenji Watanabe (National Institute for Materials Science) ; Takashi Taniguchi (National Institute for Materials Science) ; Fan Zhang ; Marc Bockrath ; Chun Ning Lau

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Emilio Codecido, Qiyue Wang, Ryan Koester, Shi Che, Haidong Tian, Rui Lv, Son Tran, Kenji Watanabe, Takashi Taniguchi, Fan Zhang, Marc Bockrath, Chun Ning Lau. Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle. Science Advances. 2019, 5 (9), . https://doi.org/10.1126/sciadv.aaw9770

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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.

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