Untying the insulating and superconducting orders in magic-angle graphene

Petr Stepanov, Ipsita Das, Xiaobo Lu, Ali Fahimniya, Kenji Watanabe, Takashi Taniguchi, Frank H. L. Koppens, Johannes Lischner, Leonid Levitov and Dmitri K. Efetov ()
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Petr Stepanov: The Barcelona Institute of Science and Technology
Ipsita Das: The Barcelona Institute of Science and Technology
Xiaobo Lu: The Barcelona Institute of Science and Technology
Ali Fahimniya: Massachusetts Institute of Technology
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Frank H. L. Koppens: The Barcelona Institute of Science and Technology
Johannes Lischner: Imperial College London
Leonid Levitov: Massachusetts Institute of Technology
Dmitri K. Efetov: The Barcelona Institute of Science and Technology

Nature, 2020, vol. 583, issue 7816, 375-378

Abstract: Abstract The coexistence of superconducting and correlated insulating states in magic-angle twisted bilayer graphene1–11 prompts fascinating questions about their relationship. Independent control of the microscopic mechanisms that govern these phases could help uncover their individual roles and shed light on their intricate interplay. Here we report on direct tuning of electronic interactions in this system by changing the separation distance between the graphene and a metallic screening layer12,13. We observe quenching of correlated insulators in devices with screening layer separations that are smaller than the typical Wannier orbital size of 15 nanometres and with twist angles that deviate slightly from the magic angle of 1.10 ± 0.05 degrees. Upon extinction of the insulating orders, the vacated phase space is taken over by superconducting domes that feature critical temperatures comparable to those in devices with strong insulators. In addition, we find that insulators at half-filling can reappear in small out-of-plane magnetic fields of 0.4 tesla, giving rise to quantized Hall states with a Chern number of 2. Our study suggests re-examination of the often-assumed ‘parent-and-child’ relation between the insulating and superconducting phases in moiré graphene, and suggests a way of directly probing the microscopic mechanisms of superconductivity in strongly correlated systems.

Date: 2020
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DOI: 10.1038/s41586-020-2459-6

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