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Title: Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene

Abstract

The discovery of superconducting and insulating states in magic-angle twisted bilayer graphene (MATBG) has ignited considerable interest in understanding the nature of electronic interactions in this chemically pristine material. The transport properties of MATBG as a function of doping are similar to those of high-transition-temperature copper oxides and other unconventional superconductors which suggests that MATBG may be a highly interacting system. However, to our knowledge, there is no direct experimental evidence of strong many-body correlations in MATBG. Here we present high-resolution spectroscopic measurements, obtained using a scanning tunnelling microscope, that provide such evidence as a function of carrier density. MATBG displays unusual spectroscopic characteristics that can be attributed to electron–electron interactions over a wide range of doping levels, including those at which superconductivity emerges in this system. We show that our measurements cannot be explained with a mean-field approach for modelling electron–electron interactions in MATBG. The breakdown of a mean-field approach when applied to other correlated superconductors, such as copper oxides, has long inspired the study of the highly correlated Hubbard model3. We show that a phenomenological extended-Hubbard-model cluster calculation, which is motivated by the nearly localized nature of the relevant electronic states of MATBG, produces spectroscopic features that aremore » similar to those that we observed experimentally. Finally, our findings demonstrate the critical role of many-body correlations in understanding the properties of MATBG.« less

Authors:
 [1];  [2];  [1];  [1];  [1];  [3];  [3];  [1]; ORCiD logo [1]
  1. Princeton Univ., NJ (United States). Joseph Henry Lab., and Dept. of Physics
  2. Princeton Univ., NJ (United States). Princeton Center for Theoretical Science
  3. National Inst. for Materials Science (NIMS), Tsukuba (Japan)
Publication Date:
Research Org.:
Princeton Univ., NJ (United States); National Institute for Materials Science (NIMS), Tsukuba (Japan)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES); Gordon and Betty Moore Foundation (GBMF); National Science Foundation (NSF); Packard Foundation; Simons Investigator Award; Schmidt Fund
OSTI Identifier:
1686117
Alternate Identifier(s):
OSTI ID: 1574996
Grant/Contract Number:  
FG02-07ER46419; SC0016239; DMR-1643312; DMR-1420541
Resource Type:
Accepted Manuscript
Journal Name:
Nature (London)
Additional Journal Information:
Journal Name: Nature (London); Journal Volume: 572; Journal Issue: 7767; Journal ID: ISSN 0028-0836
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; spectroscopic; magic-angle; twisted bilayer graphene; physics; electronic properties; electronic materials; superconductivity; superconducting materials; superconducting properties

Citation Formats

Xie, Yonglong, Lian, Biao, Jäck, Berthold, Liu, Xiaomeng, Chiu, Cheng-Li, Watanabe, Kenji, Taniguchi, Takashi, Bernevig, B. Andrei, and Yazdani, Ali. Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene. United States: N. p., 2019. Web. https://doi.org/10.1038/s41586-019-1422-x.
Xie, Yonglong, Lian, Biao, Jäck, Berthold, Liu, Xiaomeng, Chiu, Cheng-Li, Watanabe, Kenji, Taniguchi, Takashi, Bernevig, B. Andrei, & Yazdani, Ali. Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene. United States. https://doi.org/10.1038/s41586-019-1422-x
Xie, Yonglong, Lian, Biao, Jäck, Berthold, Liu, Xiaomeng, Chiu, Cheng-Li, Watanabe, Kenji, Taniguchi, Takashi, Bernevig, B. Andrei, and Yazdani, Ali. Wed . "Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene". United States. https://doi.org/10.1038/s41586-019-1422-x. https://www.osti.gov/servlets/purl/1686117.
@article{osti_1686117,
title = {Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene},
author = {Xie, Yonglong and Lian, Biao and Jäck, Berthold and Liu, Xiaomeng and Chiu, Cheng-Li and Watanabe, Kenji and Taniguchi, Takashi and Bernevig, B. Andrei and Yazdani, Ali},
abstractNote = {The discovery of superconducting and insulating states in magic-angle twisted bilayer graphene (MATBG) has ignited considerable interest in understanding the nature of electronic interactions in this chemically pristine material. The transport properties of MATBG as a function of doping are similar to those of high-transition-temperature copper oxides and other unconventional superconductors which suggests that MATBG may be a highly interacting system. However, to our knowledge, there is no direct experimental evidence of strong many-body correlations in MATBG. Here we present high-resolution spectroscopic measurements, obtained using a scanning tunnelling microscope, that provide such evidence as a function of carrier density. MATBG displays unusual spectroscopic characteristics that can be attributed to electron–electron interactions over a wide range of doping levels, including those at which superconductivity emerges in this system. We show that our measurements cannot be explained with a mean-field approach for modelling electron–electron interactions in MATBG. The breakdown of a mean-field approach when applied to other correlated superconductors, such as copper oxides, has long inspired the study of the highly correlated Hubbard model3. We show that a phenomenological extended-Hubbard-model cluster calculation, which is motivated by the nearly localized nature of the relevant electronic states of MATBG, produces spectroscopic features that are similar to those that we observed experimentally. Finally, our findings demonstrate the critical role of many-body correlations in understanding the properties of MATBG.},
doi = {10.1038/s41586-019-1422-x},
journal = {Nature (London)},
number = 7767,
volume = 572,
place = {United States},
year = {2019},
month = {7}
}

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Cited by: 52 works
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Figures / Tables:

Figure 1 Figure 1: Non-interacting spectroscopic properties of MATBG. a, Schematic of the STM measurement setup on MATBG devices. b, Optical image of the device. c, STM topography showing the moiré superlattice with θ=1.01°. d, STM spectrum measured on an AA site for slight electron doping (Vg= -4V, Vset=200mV, Iset=120pA, Vmod=1mV). Themore » blue and green arrows mark the step-like features. e, Band structure calculated using the continuum model including the effects of strain and relaxation. ΓMΛm is a non-high symmetry direction along which the Dirac points (locally protected by C2zT symmetry) are located. The black dotted line indicates the Fermi level. The blue (green) dashed line corresponds to the vHs of the first conduction (valence) remote band. f, Corresponding sqrt(LDOS) (offset by -17meV) calculated on an AA site. The blue and green arrows mark the vHs of the first conduction and valence remote bands.« less

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    Large-area, periodic, and tunable intrinsic pseudo-magnetic fields in low-angle twisted bilayer graphene
    journal, January 2020


    Dynamic band structure and capacitance effects in scanning tunneling spectroscopy of bilayer graphene
    journal, October 2019

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    Graphene-based spinmechatronic valve
    journal, October 2019


    Electronic band structure and pinning of Fermi energy to Van Hove singularities in twisted bilayer graphene: A self-consistent approach
    journal, November 2019


    Attractive electron-electron interactions from internal screening in magic-angle twisted bilayer graphene
    journal, December 2019


    Collective Excitations of Quantum Anomalous Hall Ferromagnets in Twisted Bilayer Graphene
    journal, January 2020


    Nature of the Correlated Insulator States in Twisted Bilayer Graphene
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