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; Feng Wang

doi:10.1038/s41586-019-1393-y

Signatures of tunable superconductivity in a trilayer graphene moiré superlattice

Nature. 2019 Aug;572(7768):215-219. doi: 10.1038/s41586-019-1393-y. Epub 2019 Jul 17.

Authors

Guorui Chen^#^{1

2}, Aaron L Sharpe^#^{3

4}, Patrick Gallagher^{1

2}, Ilan T Rosen^{3

4}, Eli J Fox^{4

5}, Lili Jiang², Bosai Lyu^{6

7}, Hongyuan Li^{6

7}, Kenji Watanabe⁸, Takashi Taniguchi⁸, Jeil Jung⁹, Zhiwen Shi^{6

7}, David Goldhaber-Gordon^{10

11}, Yuanbo Zhang^{12

13

14}, Feng Wang^{15

16

17}

Affiliations

¹ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
² Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
³ Department of Applied Physics, Stanford University, Stanford, CA, USA.
⁴ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
⁵ Department of Physics, Stanford University, Stanford, CA, USA.
⁶ Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China.
⁷ Collaborative Innovation Center of Advanced Microstructures, Nanjing, China.
⁸ National Institute for Materials Science, Tsukuba, Japan.
⁹ Department of Physics, University of Seoul, Seoul, South Korea.
¹⁰ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA. goldhaber-gordon@stanford.edu.
¹¹ Department of Physics, Stanford University, Stanford, CA, USA. goldhaber-gordon@stanford.edu.
¹² Collaborative Innovation Center of Advanced Microstructures, Nanjing, China. zhyb@fudan.edu.cn.
¹³ State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, China. zhyb@fudan.edu.cn.
¹⁴ Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai, China. zhyb@fudan.edu.cn.
¹⁵ Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. fengwang76@berkeley.edu.
¹⁶ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. fengwang76@berkeley.edu.
¹⁷ Kavli Energy NanoSciences Institute at the University of California, Berkeley, CA, USA. fengwang76@berkeley.edu.

^# Contributed equally.

PMID: 31316203
DOI: 10.1038/s41586-019-1393-y

Abstract

Understanding the mechanism of high-transition-temperature (high-T_c) superconductivity is a central problem in condensed matter physics. It is often speculated that high-T_c superconductivity arises in a doped Mott insulator¹ as described by the Hubbard model^2-4. 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 superlattice^5,6 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.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.