2025/05/05 by Zhang, Yichao, Ahammed, Ballal, Bae, Sang Hyun +7
#FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci)
paper · doi:10.48550/arxiv.2505.03060
Twisted 2D materials exhibit unique vibrational modes called moiré phonons, which arise from the moiré superlattice. Here, we demonstrate atom-by-atom imaging of phasons, an ultrasoft class of moiré 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 moiré 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 moiré phonon physics.