Title: Signatures of tunable superconductivity in a trilayer graphene moiré superlattice

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 belowmore » 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.« less

Authors:

Chen, Guorui ^[1]; Sharpe, Aaron L. ^[2]; Gallagher, Patrick ^[1]; Rosen, Ilan T. ^[2]; Fox, Eli J. ^[3]; Jiang, Lili ^[4]; Lyu, Bosai ^[5]; Li, Hongyuan ^[5]; Watanabe, Kenji ^[6]; Taniguchi, Takashi ^[6]; Jung, Jeil ^[7]; Shi, Zhiwen ^[5]; Goldhaber-Gordon, David ^[3]; Zhang, Yuanbo ^[8]; Wang, Feng ^[1]

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+ Show Author Affiliations

1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
2. Stanford Univ., CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
3. SLAC National Accelerator Lab., Menlo Park, CA (United States); Stanford Univ., CA (United States)
4. Univ. of California, Berkeley, CA (United States)
5. Shanghai Jiao Tong Univ. (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)
6. National Inst. for Materials Science (NIMS), Tsukuba (Japan)
7. Univ. of Seoul, Seoul (Korea, Republic of)
8. Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Fudan Univ., Shanghai (China)

Publication Date:

2019-07-17

Research Org.:

Energy Frontier Research Centers (EFRC) (United States). Center for Novel Pathways to Quantum Coherence in Materials (NPQC); Stanford Univ., Redwood City, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division

OSTI Identifier:

1545526

Alternate Identifier(s):

OSTI ID: 1619126

Grant/Contract Number:  

AC02-76SF00515; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Nature (London)

Additional Journal Information:

Journal Name: Nature (London); Journal Volume: 572; Journal Issue: 7768; Journal ID: ISSN 0028-0836

Publisher:

Nature Publishing Group

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY