Light causes atomic layers to do the twist in moiré materials

Amazing stuff!

"In brief

• A new study shows that light can control the twisting motion of atomic layers in moiré materials, allowing for novel material manipulation techniques.
• Researchers used ultrafast electron diffraction to observe atomic dynamics in real time, offering groundbreaking insights into the behavior of materials.

...

A pulse of light sets the tempo in the material. Atoms in a crystalline sheet just a few atoms thick begin to move – not randomly, but in a coordinated rhythm, twisting and untwisting in sync like dancers following a beat. ..."

From the abstract:

"Two-dimensional moiré materials are formed by artificially stacking atomically thin monolayers. Correlated and topological quantum phases can be engineered by precise choice of stacking geometry. These designer electronic properties depend crucially on interlayer coupling and atomic registry. An open question is how the atomic registry responds on ultrafast timescales to optical excitation and whether the moiré geometry can be dynamically reconfigured to tune emergent phenomena in real time.

Here we show that femtosecond photoexcitation drives a coherent twist–untwist motion of the moiré superlattice in 2° and 57° twisted WSe2/MoSe2 heterobilayers, resolved directly by ultrafast electron diffraction.

On above-band-gap photoexcitation, the moiré superlattice diffraction features are enhanced within 1 ps and subsequently suppressed several picoseconds after, deviating markedly from typical photoinduced lattice heating.

Kinetic diffraction analysis, supported by simulations of the sample dynamics, indicates a peak-to-trough local twist angle modulation of 0.6°, correlated with a sub-THz frequency moiré phonon.

This motion is driven by ultrafast charge transfer that transiently increases interlayer attraction.

Our results could lead to ultrafast control of moiré periodic lattice distortions and, by extension, the local moiré potential that shapes excitons, polarons and correlation-driven behaviours."

Light causes atomic layers to do the twist | Stanford Report "A new study finds that light can control moiré materials, unlocking potential advances in superconductivity, magnetism, and quantum electronics."

Photoinduced twist and untwist of moiré superlattices (no public access)

Photoinduced twist and untwist of moiré superlattices in TMDC heterobilayers (preprint, open access)

Fawn Hallenbeck. Is she holding up an ancient Chinese mirror? 😊 Notice the bamboo in the background. Nice photo