Ultrafast formation of domain walls of a charge density wave in SmTe3

We study ultrafast x-ray diffraction on the charge density wave (CDW) of SmTe3 using an x-ray free-electron laser. The high momentum and time resolution afforded by the x-ray laser enabled capturing fine wave-vector and time-dependent features of the CDW that originate from fast (in time) and sharp (in real space) variations of the CDW lattice distortion, which we attribute to an inversion of the order parameter. These domain inversions occur near the surface and are caused by the short penetration depth of the near-infrared pump with the wavelength centered at 800 nm, resulting in CDW domain walls perpendicular to the sample surface. These domain walls break the CDW long-range order on the scale of the x-ray probe depth, controlled experimentally by the x-ray incidence angle and suppress the diffraction intensity of the CDW for times much longer than the similar to 1-ps recovery of the electronic gap observed in time and angle-resolved photoemission spectroscopy. We model the spatial and temporal dependences of the order parameter using a simple Ginzburg-Landau model with all the parameters obtained from the published literature. We find reasonable agreement between the calculated and the measured diffraction across the momentum, time, fluence, and incidence angle dependence without adjusting any parameters. We reconstruct the spatial and temporal dependences of the lattice order parameter and find that at long times, depending on the pump fluence, multiple domain walls remain at distances of a few nanometers from the surface.

Automated summary

The study utilizing an X-ray free-electron laser on the charge density wave (CDW) of SmTe3 discovered domain inversions occurring near the surface, attributed to the short penetration depth of the infrared pump leading to CDW domain walls a few nanometers from the surface. These domain walls suppress the diffraction intensity of CDW by controlling the X-ray incidence angle.