Phase-ordering of charge density waves traced by ultrafast low-energy electron diffraction

TL;DR

This study introduces ultrafast low-energy electron diffraction (ULEED) to observe surface charge density wave phase transitions in 1T-TaS2, revealing phase-ordering kinetics and defect dynamics with high spatial resolution.

Contribution

The paper demonstrates the application of backscattering ULEED for real-time analysis of surface charge-density wave phase transitions and phase-ordering kinetics.

Findings

Power-law scaling of correlation length during phase coarsening

Dislocation-type topological defects drive the ordering process

Ultrafast diffraction enables surface structural dynamics study

Abstract

We introduce ultrafast low-energy electron diffraction (ULEED) in backscattering for the study of structural dynamics at surfaces. Using a tip-based source of ultrashort electron pulses, we investigate the optically-driven transition between charge-density wave phases at the surface of 1T-TaS2. The large transfer width of the instrument allows us to employ spot-profile analysis, resolving the phase-ordering kinetics in the nascent incommensurate charge-density wave phase. We observe a coarsening that follows a power-law scaling of the correlation length, driven by the annihilation of dislocation-type topological defects of the charge-ordered lattice. Our work opens up the study of a wide class of structural transitions and ordering phenomena at surfaces and in low-dimensional systems.