Spectroscopy of a tunable moiré system with a correlated and topological flat band

• Published in: Nature communications Vol. 12; no. 1; pp. 2732 - 7
• Main Authors: Liu, Xiaomeng, Chiu, Cheng-Li, Lee, Jong Yeon, Farahi, Gelareh, Watanabe, Kenji, Taniguchi, Takashi, Vishwanath, Ashvin, Yazdani, Ali
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 12.05.2021; Nature Publishing Group; Nature Portfolio
• Subjects: 147/138; 639/766/119/2792; 639/766/119/995; 639/925/918/1052; Band structure of solids; Bilayers; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Continuum modeling; Correlation; Crystals; Electric fields; Electron states; electronic properties and devices; electronic properties and materials; Graphene; Humanities and Social Sciences; Magnetic fields; MATERIALS SCIENCE; multidisciplinary; Scanning; Scanning tunneling microscopy; Science; Science (multidisciplinary); Spectral signatures; Spectroscopy; Spectrum analysis; Superlattices; topological matter; Topology
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-021-23031-0

Moiré superlattices created by the twisted stacking of two-dimensional crystals can host electronic bands with flat energy dispersion in which enhanced interactions promote correlated electron states. The twisted double bilayer graphene (TDBG), where two Bernal bilayer graphene are stacked with a twist angle, is such a moiré system with tunable flat bands. Here, we use gate-tuned scanning tunneling spectroscopy to directly demonstrate the tunability of the band structure of TDBG with an electric field and to show spectroscopic signatures of electronic correlations and topology for its flat band. Our spectroscopic experiments are in agreement with a continuum model of TDBG band structure and reveal signatures of a correlated insulator gap at partial filling of its isolated flat band. The topological properties of this flat band are probed with the application of a magnetic field, which leads to valley polarization and the splitting of Chern bands with a large effective g-factor. Twisted double bilayer graphene hosts flat bands that can be tuned with an electric field. Here, by using gate-tuned scanning tunneling spectroscopy, the authors demonstrate the tunability of the flat band and reveal spectral signatures of correlated electron states and the topological nature of the flat band.