Giant Atomic Swirl in Graphene Bilayers with Biaxial Heterostrain

This work was carried out as part of a collaboration between several laboratories: PHELIQS and IRIG-MEM (CEA, Univ. Grenoble Alpes, Grenoble), Department of Physics and Astronomy (Univ. of Manchester), Imdea Nanoscience (Madrid), Donostia International Physics Center (San Sebastián), CRHEA (Université Côte d’Azur, CNRS) and LPTM (CY Cergy Paris Université, CNRS, Cergy-Pontoise).

The study of moiré engineering started with the advent of van der Waals heterostructures, in which stacking 2D 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. A twist is now routinely used to adjust the properties of 2D materials. This study investigates 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 forthe next step of moiré engineering in van der Waals multilayers.

Advanced Materials : https://doi.org/10.1002/adma.202306312

Auteurs :

Florie Mesple, Niels R. Walet, Guy Trambly de Laissardière, Francisco Guinea, Djordje Došenović, Hanako Okuno, Colin Paillet, Adrien Michon, Claude Chapelier, Vincent T. Renard