Atom-by-atom Imaging of Moir\'e Phasons using Electron Ptychography

TL;DR

This study uses ultrahigh-resolution electron ptychography to image and analyze moiré phasons in twisted bilayer WSe2 at atomic scale, revealing their vibrational properties and dominance in thermal vibrations.

Contribution

It introduces atom-by-atom imaging of moiré phasons in twisted bilayer WSe2, combining experimental imaging with simulations to understand their vibrational behavior.

Findings

Moiré phasons exhibit increased vibrational amplitudes at solitons and AA regions.

Phasons dominate thermal vibrations in low-angle twisted bilayers.

Ultrahigh-resolution imaging reveals detailed phonon properties at atomic scale.

Abstract

Twisted 2D materials exhibit unique vibrational modes called moir\'e phonons, which arise from the moir\'e superlattice. Here, we demonstrate atom-by-atom imaging of phasons, an ultrasoft class of moir\'e phonons in twisted bilayer WSe2. Using ultrahigh-resolution (<15 pm) electron ptychography, we image the size and shape of each atom to extract time-averaged vibrational amplitudes as a function of twist angle and position. We observe several signature properties of moir\'e phasons, such as increased vibrational amplitudes at solitons and AA-stacked regions. By correlating experiments with molecular dynamics simulations and lattice dynamics calculations, we show phasons dominate the thermal vibrations in low-angle twisted bilayers. These results represent a powerful route to image thermal vibrations at atomic resolution, unlocking experimental studies of a thus-far hidden branch of moir\'e phonon physics.