Visualization of the flat electronic band in twisted bilayer graphene near the magic angle twist

MIB Utama and RJ Koch and K Lee and N Leconte and HY Li and SH Zhao and LL Jiang and JY Zhu and K Watanabe and T Taniguchi and PD Ashby and A Weber-Bargioni and A Zettl and C Jozwiak and J Jung and E Rotenberg and A Bostwick and F Wang, NATURE PHYSICS, 17, 184-+ (2021).

DOI: 10.1038/s41567-020-0974-x

Bilayer graphene has been predicted to host a moire miniband with flat dispersion if the layers are stacked at specific twist angles known as the 'magic angles'(1,2). Recently, twisted bilayer graphene (tBLG) with a magic angle twist was reported to exhibit a correlated insulating state and superconductivity(3,4), where the presence of the flat miniband in the system is thought to be essential for the emergence of these ordered phases in the transport measurements. Although tunnelling spectroscopy(5-9)and electronic compressibility measurements(10)in tBLG have found a van Hove singularity that is consistent with the presence of the flat miniband, a direct observation of the flat dispersion in the momentum space of such a moire miniband in tBLG is still lacking. Here, we report the visualization of this flat moire miniband by using angle- resolved photoemission spectroscopy with nanoscale resolution. The high spatial resolution of this technique enabled the measurement of the local electronic structure of the tBLG. The measurements demonstrate the existence of the flat moire band near the charge neutrality for tBLG close to the magic angle at room temperature. The flat electronic bands that are associated with ordered phases in twisted bilayer graphene at a magic twist angle have been imaged using angle-resolved photoemission spectroscopy.

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