Programme

I.11 -- Invited, VCTP-46

Date: Wednesday, 6 October 2021

Time: 16:00 - 16:30

Lattice dynamics and electronic properties of small-angle twisted bilayer graphene

Viet-Hung Nguyen

Université catholique de Louvain (UCLouvain), Louvain-la-Neuve, Belgium

Twisted bilayer graphene (TBLG) is created by rotating the two crystal layers in bilayer graphene with respect to each other. Owning to the outstanding and nicely tunable properties, TBLGs display many fascinating features, especially, those related to the electronic flat bands and the corresponding strong electronic localization observed when the twist angle is close to magic ones. Indeed, superconductivity, correlated insulating states, magnetism, and quantized anomalous Hall states have been explored in magic-angle TBLGs (see the recent review [1] and references therein), thus giving rise to the nascent research field of “twistronics”.
In this context, a good understanding of the intrinsic electronic properties and lattice vibrations as well as electron-phonon interactions within these graphene systems has been highly desirable in recent years. In this talk, I will present the recent studies [2-4] on these fundamental properties of small-angle TBLGs. At small twist angles ≲ 1.1°, TBLGs undergo a self-organized lattice reconstruction [5], strongly modifying their stacking structure with the presence of a domain wall network. The stacking structure of TBLG at small twist angles is hence very different from that of large angle ones where the moiré superlattice evolves smoothly. The resulting reconstructed superlattice significantly modulates the vibrational and electronic structures within the material, leading to changes in the behavior of electron-phonon coupling and to the observation of strong correlations and superconductivity. These features have been explored and slolidly clarified by both Raman spectrocopies and theoretical simulations [2-4]. In addition, our works [3,4] analyzing both global and local quantities provide a comprehensive and accurate understanding of the electronic properties of small-angle TBLG systems. Especially, the contradiction between the theoretical and experimental studies previously published on the emergence of small magic angles < 1.1° has been solidly clarified [3].
REFERENCES:
[1] E. Y. Andrei and A. H. MacDonald, Nat. Mater. 19, 1265-1275 (2020)
[2] M. Lamparski et al., 2D Mater. 7, 025050 (2020); DOI:10.1088/2053-1583/ab7874
[3] V. Hung Nguyen et al., 2D Mater. 8, 035046 (2021); DOI:10.1088/2053-1583/ac044f
[4] A. C. Gadelha et al., Nature 590, 405-409 (2021); DOI:10.1038/s41586-021-03252-5
[5] H. Yoo et al., Nat. Mater. 18, 448-453 (2019)

Presenter: Nguyen Viet Hung