Discovery of Phasons

Phasons - collective sliding modes first identified in quasicrystals in the 1980s - had remained a curiosity of aperiodic systems. We discovered that they emerge universally in moiré materials, appearing as two additional sound-wave-like phonon modes beyond the three acoustic branches found in conventional crystals. (See left animation above.) Our predictions were recently experimentally verified in  Science by Prof. Pinshane Huang’s group using ultra-high-resolution electron ptychography. 

We further revealed that thermally activated phasons create interference patterns that coherently amplify electron-phonon coupling - enabling electrons and excitons to "surf" on these collective vibrations. This manifests as anomalous spatial and temporal spreading of excitons at low temperatures, breaking the expected Arrhenius behavior. (See right animation above.) Our work has been featured in news coverage by Phys.org, SciTech Daily, EurekAlert!, and other outlets.

This discovery opens new pathways for controlling quantum transport in moiré systems. 

Publications: Phys. Rev. Research, Nano Lett., and ACS Nano. 

Current & Recent Collaborators:

Theory: Manish Jain (IISc), Johannes Lischner and Arash Mostofi (Imperial College). 

Experiment: Archana Raja (Berkeley), Antonio Rossi (IIT Pisa).