Giant Atomic Swirl in Graphene Bilayers with Biaxial Heterostrain

Abstract

The study of moiré engineering started with the advent of van der Waals heterostructures in which stacking two‐dimensional layers with different lattice constants leads to a moiré pattern controlling their electronic properties. The field entered a new era when it was found that adjusting the twist between two graphene layers led to strongly‐correlated‐electron physics and topological effects associated with atomic relaxation. Twist is now used routinely to adjust the properties of two‐dimensional materials. Here, we investigate a new type of moiré superlattice in bilayer graphene when one layer is biaxially strained with respect to the other ‐ so‐called biaxial heterostrain. Scanning tunneling microscopy measurements uncover spiraling electronic states associated with a novel symmetry‐breaking atomic reconstruction at small biaxial heterostrain. Atomistic calculations using experimental parameters as inputs reveal that a giant atomic swirl forms around regions of aligned stacking to reduce the mechanical energy of the bilayer. Tight‐binding calculations performed on the relaxed structure show that the observed electronic states decorate spiraling domain wall solitons as required by topology. This study establishes biaxial heterostrain as an important parameter to be harnessed for the next step of moiré engineering in van der Waals multilayers.This article is protected by copyright. All rights reserved

Kagome Quantum Oscillations in Graphene Superlattices

“…This is because LT contours in low-symmetry crystals have the form of quasi-1D block-chains of intertwining meanders , which do not provide pairs of paths needed for the energy-independent Aharonov–Bohm interference. Therefore, breaking the C 3 rotational symmetry of the mSL by straining one of the 2D crystals in a stack , and violating the kagome topology of the LT network would suppress these novel low-magnetic-field high-temperature quantum oscillations.…”

Competition of Moiré Network Sites to Form Electronic Quantum Dots in Reconstructed MoX2/WX2 Heterostructures

“…In this paper, we demonstrate a high sensitivity of the band edge properties of marginally twisted (small angle |θ| < 1°) MoX 2 /WX 2 bilayers to the lattice reconstruction and DWN formation. Recently, it has been noted that, while the nodes of such DWNs represent the areas of the largest strain, both hydrostatic (lattice dilation in MoX 2 vs compression in WX 2 ) and shear, ,− the higher energetic cost of hydrostatic strain can be reduced by transforming some dilation/compression into shear achieved via “twirling” of DWN, − as marked on the maps in Figure . Here, we highlight the role of hydrostatic strain, because it causes stronger band edge shifts than shear deformations ,− (inset of Figure ), hence affecting electron and hole confinement across the reconstructed moiré structure.…”