Signatures of tunable superconductivity in a trilayer graphene moiré superlattice

Guorui Chen, Aaron L. Sharpe, Patrick Gallagher, Ilan T. Rosen, Eli J. Fox, Lili Jiang, Bosai Lyu, Hongyuan Li, Kenji Watanabe, Takashi Taniguchi, Jeil Jung, Zhiwen Shi, David Goldhaber-Gordon (), Yuanbo Zhang () and Feng Wang ()
Additional contact information
Guorui Chen: Lawrence Berkeley National Laboratory
Aaron L. Sharpe: Stanford University
Patrick Gallagher: Lawrence Berkeley National Laboratory
Ilan T. Rosen: Stanford University
Eli J. Fox: SLAC National Accelerator Laboratory
Lili Jiang: University of California at Berkeley
Bosai Lyu: Shanghai Jiao Tong University
Hongyuan Li: Shanghai Jiao Tong University
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Jeil Jung: University of Seoul
Zhiwen Shi: Shanghai Jiao Tong University
David Goldhaber-Gordon: SLAC National Accelerator Laboratory
Yuanbo Zhang: Collaborative Innovation Center of Advanced Microstructures
Feng Wang: Lawrence Berkeley National Laboratory

Nature, 2019, vol. 572, issue 7768, 215-219

Abstract: Abstract Understanding the mechanism of high-transition-temperature (high-Tc) superconductivity is a central problem in condensed matter physics. It is often speculated that high-Tc superconductivity arises in a doped Mott insulator1 as described by the Hubbard model2–4. An exact solution of the Hubbard model, however, is extremely challenging owing to the strong electron–electron correlation in Mott insulators. Therefore, it is highly desirable to study a tunable Hubbard system, in which systematic investigations of the unconventional superconductivity and its evolution with the Hubbard parameters can deepen our understanding of the Hubbard model. Here we report signatures of tunable superconductivity in an ABC-trilayer graphene (TLG) and hexagonal boron nitride (hBN) moiré superlattice. Unlike in ‘magic angle’ twisted bilayer graphene, theoretical calculations show that under a vertical displacement field, the ABC-TLG/hBN heterostructure features an isolated flat valence miniband associated with a Hubbard model on a triangular superlattice5,6 where the bandwidth can be tuned continuously with the vertical displacement field. Upon applying such a displacement field we find experimentally that the ABC-TLG/hBN superlattice displays Mott insulating states below 20 kelvin at one-quarter and one-half fillings of the states, corresponding to one and two holes per unit cell, respectively. Upon further cooling, signatures of superconductivity (‘domes’) emerge below 1 kelvin for the electron- and hole-doped sides of the one-quarter-filling Mott state. The electronic behaviour in the ABC-TLG/hBN superlattice is expected to depend sensitively on the interplay between the electron–electron interaction and the miniband bandwidth. By varying the vertical displacement field, we demonstrate transitions from the candidate superconductor to Mott insulator and metallic phases. Our study shows that ABC-TLG/hBN heterostructures offer attractive model systems in which to explore rich correlated behaviour emerging in the tunable triangular Hubbard model.

Date: 2019
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DOI: 10.1038/s41586-019-1393-y

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