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

Journal Article · 31 July 2019 · Nature (London)

DOI: https://doi.org/10.1038/s41586-019-1422-x · OSTI ID:1686117

Xie, Yonglong ^[1]; Lian, Biao ^[2]; Jäck, Berthold ^[1]; Liu, Xiaomeng ^[1]; Chiu, Cheng-Li ^[1]; Watanabe, Kenji ^[3]; Taniguchi, Takashi ^[3]; Bernevig, B. Andrei ^[1]; Yazdani, Ali  ^[1]

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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)

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.

• Research Organization: Princeton Univ., NJ (United States); National Institute for Materials Science (NIMS), Tsukuba (Japan)
• Sponsoring Organization: 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; USDOE
• Grant/Contract Number: FG02-07ER46419; SC0016239; DMR-1643312; DMR-1420541
• OSTI ID: 1686117
• Alternate ID(s): OSTI ID: 1574996
• Journal Information: Nature (London), Vol. 572, Issue 7767; ISSN 0028-0836
• Publisher: Nature Publishing GroupCopyright Statement
• Country of Publication: United States
• Language: English