Imaging moir\xe9 deformation and dynamics in twisted bilayer graphene

Tobias A De Jong,Sense Jan Van Der Molen,Milan P Allan,Tjerk Benschop,Rudolf M Tromp,Xingchen Chen,Eugene E Krasovskii,Michiel J A De Dood

doi:10.1038/s41467-021-27646-1

Tobias A De Jong, Sense Jan Van Der Molen + Show 6 more

Open Access

https://doi.org/10.1038/s41467-021-27646-1

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Journal: Nature Communications	Publication Date: Jan 10, 2022
Citations: 18	License type: open-access

Affiliation: Leiden University

Abstract

In ‘magic angle’ twisted bilayer graphene (TBG) a flat band forms, yielding correlated insulator behavior and superconductivity. In general, the moiré structure in TBG varies spatially, influencing the overall conductance properties of devices. Hence, to understand the wide variety of phase diagrams observed, a detailed understanding of local variations is needed. Here, we study spatial and temporal variations of the moiré pattern in TBG using aberration-corrected Low Energy Electron Microscopy (AC-LEEM). We find a smaller spatial variation than reported previously. Furthermore, we observe thermal fluctuations corresponding to collective atomic displacements over 70 pm on a timescale of seconds. Remarkably, no untwisting is found up to 600 ∘C. We conclude that thermal annealing can be used to decrease local disorder. Finally, we observe edge dislocations in the underlying atomic lattice, the moiré structure acting as a magnifying glass. These topological defects are anticipated to exhibit unique local electronic properties.

Highlights

In ‘magic angle’ twisted bilayer graphene (TBG) a flat band forms, yielding correlated insulator behavior and superconductivity
Local variation in twist angle and strain in TBG will directly influence the result of such experiments
To understand the wide variation observed in the phase diagrams and critical temperatures, a more detailed understanding of the local moiré variation is needed[10]

Summary

Introduction

In ‘magic angle’ twisted bilayer graphene (TBG) a flat band forms, yielding correlated insulator behavior and superconductivity. Local variation in twist angle and strain in TBG will directly influence the result of such experiments. At 500 ∘C, we observe thermal fluctuations of the moiré lattice, corresponding to collective atomic displacements of less than 70 pm on a time scale of seconds[22].

Results

Conclusion