Cascade of electronic transitions in magic-angle twisted bilayer graphene
| Autor: | Sangjun Jeon, Ali Yazdani, Biao Lian, Yonglong Xie, Dillon Wong, Kenji Watanabe, B. Andrei Bernevig, Myungchul Oh, Kevin P. Nuckolls, Takashi Taniguchi |
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| Rok vydání: | 2020 |
| Předmět: |
FOS: Physical sciences
02 engineering and technology Electron 01 natural sciences law.invention Superconductivity (cond-mat.supr-con) Condensed Matter - Strongly Correlated Electrons law Mesoscale and Nanoscale Physics (cond-mat.mes-hall) 0103 physical sciences Degeneracy (biology) 010306 general physics Spin (physics) Physics Superconductivity Multidisciplinary Strongly Correlated Electrons (cond-mat.str-el) Condensed Matter - Mesoscale and Nanoscale Physics Condensed matter physics Condensed Matter - Superconductivity Degenerate energy levels Landau quantization 021001 nanoscience & nanotechnology Scanning tunneling microscope 0210 nano-technology Bilayer graphene |
| Zdroj: | Nature. 582:198-202 |
| ISSN: | 1476-4687 0028-0836 |
| DOI: | 10.1038/s41586-020-2339-0 |
| Popis: | Magic-angle twisted bilayer graphene (MATBG) exhibits a rich variety of electronic states, including correlated insulators, superconductors, and topological phases. Understanding the microscopic mechanisms responsible for these phases requires determining the interplay between electron-electron interactions and quantum degeneracy due to spin and valley degrees of freedom. Signatures of strong electron-electron correlations have been observed at partial fillings of the flat electronic bands in recent spectroscopic measurements. Transport experiments have shown changes in the Landau level degeneracy at fillings corresponding to an integer number of electrons per moir\'e unit cell. However, the interplay between interaction effects and the degeneracy of the system is currently unclear. Using high-resolution scanning tunneling microscopy (STM), we observed a cascade of transitions in the spectroscopic properties of MATBG as a function of electron filling. We find distinct changes in the chemical potential and a rearrangement of the low-energy excitations at each integer filling of the moir\'e flat bands. These spectroscopic features are a direct consequence of Coulomb interactions, which split the degenerate flat bands into Hubbard sub-bands. We find these interactions, the strength of which we can extract experimentally, to be surprisingly sensitive to the presence of a perpendicular magnetic field, which strongly modifies the spectroscopic transitions. The cascade of transitions we report here characterizes the correlated high-temperature parent phase from which various insulating and superconducting ground-state phases emerge at low temperatures in MATBG. |
| Databáze: | OpenAIRE |
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