An Atomistic Insight into Moiré Reconstruction in Twisted Bilayer Graphene beyond the Magic Angle

Abstract

Twisted bilayer graphene exhibits electronic properties strongly correlated with the size and arrangement of moiré patterns. While rigid rotation of the two graphene layers results in a moiré interference pattern, local rearrangements of atoms due to interlayer van der Waals interactions result in atomic reconstruction within the moiré cells. Manipulating these patterns by controlling the twist angle and externally applied strain provides a promising route to tuning their properties. Atomic reconstruction has been extensively studied for angles close to or smaller than the magic angle (θ m = 1.1°). However, this effect has not been explored for applied strain and is believed to be negligible for high twist angles. Using interpretive and fundamental physical measurements, we use theoretical and numerical analyses to resolve atomic reconstruction in angles above θ m . In addition, we propose a method to identify local regions within moiré cells and track their evolution with strain for a range of representative high twist angles. Our results show that atomic reconstruction is actively present beyond the magic angle, and its contribution to the moiré cell evolution is significant. Our theoretical method to correlate local and global phonon behavior further validates the role of reconstruction at higher angles. Our findings provide a better understanding of moiré reconstruction in large twist angles and the evolution of moiré cells under the application of strain, which might be potentially crucial for twistronics-based applications.

Uniaxial Strain-Induced Stacking Order Change in Trilayer Graphene

“…In contrast, ab initio DFT calculations, known for obtaining more accurate structural properties are computationally intensive and usually limited to smaller systems. We follow a similar approach to our previous study to monitor total energy (TE) across the length of the flake and use this measure to identify stacking configuration of atoms . We average TE for each atom with its nearest bonded neighbors to smooth energy magnitudes per atom as shown in Figure (a).…”

“…We follow a similar approach to our previous study to monitor total energy (TE) across the length of the flake and use this measure to identify stacking configuration of atoms. 62 We average TE for each atom with its nearest bonded neighbors to smooth energy magnitudes per atom as shown in Figure 3 (a). Plotting the average TE per atom along a defined path “PQ” (including the tab region) reveals two distinct regions with constant TE/atom magnitudes, separated by two energy maxima ( Figure 3 (b) for L = 40 nm).…”

Systematic DFT Modeling van der Waals Heterostructures from a Complete Configurational Basis Applied to γ-PC/WS2

“…Further, in-plane corrugations were not apparent. The phenomenon where commensurably stacked zones appear in BL vdWHs separated by highly strained soliton boundaries , was thus not encountered. This can be understood considering that the summed intralayer deformation energies of the MLs in commensurably stacked unit cells were calculated at 62 meV/Å 2 , an order of magnitude higher compared to the largest surplus of E b by configurational variation, found at −7.4 meV/Å.…”

Twisted Bilayer Graphene: A Journey Through Recent Advances and Future Perspectives

“…The electronic properties of TBG are primarily governed by the interplay between the long-range periodic potential arising from the moiré pattern and the inherent electronic properties of graphene. [63,64] When the two layers are aligned perfectly, the electronic band structures of the individual graphene layers merge, resulting in a single Dirac cone with linear dispersion. However, when the layers are twisted, a moiré superlattice is formed, leading to multiple mini-Brillouin zones and a modification of the electronic band structure (Figure 4).…”