Formation of buried domain walls in the ultrafast transition of SmTe$_3$

TL;DR

This study uses ultrafast x-ray diffraction to observe how photoexcitation induces domain walls in the charge density wave of SmTe$_3$, revealing long-lasting suppression of order and domain wall formation dynamics.

Contribution

It demonstrates the formation and propagation of domain walls in SmTe$_3$'s CDW after ultrafast excitation, modeled with a Ginzburg-Landau approach, highlighting long-lived order suppression.

Findings

Photoexcitation creates propagating domain walls in SmTe$_3$.

CDW diffraction intensity remains suppressed longer than electronic gap recovery.

Multiple domain walls can persist near the surface depending on pump fluence.

Abstract

We study ultrafast x-ray diffraction on the charge density wave (CDW) of SmTe$_3$ using an x-ray free electron laser. The CDW peaks show that photoexcitation with near-infrared pump centered at 800 nm generates domain walls of the order parameter propagating perpendicular to the sample surface. These domain walls break the CDW long range order and suppress the diffraction intensity of the CDW for times much longer than the $\sim 1$~ps recovery of the local electronic gap. We reconstruct the spatial and temporal dependence of the order parameter using a simple Ginzburg-Landau model and find good agreement between the experimental and model fluence dependences. Based on the model we find that at long times, depending on the pump fluence, multiple domain walls remain at distances of few nm from the surface.