Electronic Correlations and Superconductivity in Twisted Bilayer Graphene near Magic Angle

Twisted bilayer graphene (TBG) with a rotational misalignment (twist) angle close to the magic value of 1.1°, features isolated flat electronic bands. These bands form a strongly correlated electronic system that exhibits a range of quantum phases, including superconductivity, ferromagnetism, and correlated insulating states. In this talk, I will present the latest results from our lab on magic-angle graphene obtained using scanning tunneling microscopy/spectroscopy (STM/STS) and transport measurements [1,2]. The local spectroscopy data shows that the flat bands get highly deformed when aligned with the Fermi level. Near half-filling of the bands, we observe the development of gaps originating from correlated insulating states, while near charge neutrality, we find a regime featuring an enhanced flat band splitting that can be described within a model predicting a strong tendency towards nematic ordering. In the second part of the talk, I will discuss transport measurements using novel stack geometry showing the existence of superconductivity in the absence of insulating states. Our findings provide a basis for a microscopic understanding of correlated quantum phases in twisted bilayer graphene.
We acknowledge support from NSF (DMR-1753306 and DMR-1744011) and the Gist-Caltech memorandum of understanding program.
[1] Electronic correlations in twisted bilayer graphene near the magic angle, Y. Choi, et al.,
Nature Physics 15 (11), 1174-1180 (2019).
[2] Superconductivity without insulating states in twisted bilayer graphene stabilized by monolayer WSe2
H. Arora, R. Polski, Y. Zhang, et al., arXiv:2002.03003 (2020).