Disentangling amplitude and phase dynamics of a charge density wave in a photo-induced phase transition

TL;DR

This study investigates the ultrafast dynamics of a charge density wave in LaTe$_3$ during a photo-induced phase transition, revealing distinct amplitude recovery and phase coherence reestablishment influenced by topological defects.

Contribution

It introduces a method to independently track amplitude and phase dynamics, highlighting the role of topological defects in the phase transition process.

Findings

Rapid amplitude recovery (~1 ps) observed.

Slower phase coherence reestablishment due to defect dynamics.

Topological defects inhibit long-range order restoration.

Abstract

Upon excitation with an intense ultrafast laser pulse, a symmetry-broken ground state can undergo a non-equilibrium phase transition through pathways dissimilar from those in thermal equilibrium. Determining the mechanism underlying these photo-induced phase transitions (PIPTs) has been a long-standing issue in the study of condensed matter systems. To this end, we investigate the light-induced melting of a unidirectional charge density wave (CDW) material, LaTe$_3$. Using a suite of time-resolved probes, we independently track the amplitude and phase dynamics of the CDW. We find that a quick ($\sim\,$1$\,$ps) recovery of the CDW amplitude is followed by a slower reestablishment of phase coherence. This longer timescale is dictated by the presence of topological defects: long-range order (LRO) is inhibited and is only restored when the defects annihilate. Our results provide a framework for understanding other PIPTs by identifying the generation of defects as a governing mechanism.