Ultrafast nanoimaging of the order parameter in a structural phase transition

Optical control strategies as applied in modern-day devices are based on a profound understanding of the interplay between various degrees of freedom in out-of-equilibrium scenarios. In this context, the presence of spatial inhomogeneities is of particular interest as functionality is often based on spatially dependent response to the external stimulus. Ultrafast transmission electron microscopy (UTEM) is a powerful tool capable of unravelling such ultrafast processes in heterogeneous systems by means of imaging, diffraction and spectroscopy [1,2].

In this work, we demonstrate an experimental approach to image a structural phase transition between two charge-density wave (CDW) phases in the strongly correlated material 1T-TaS₂ on its intrinsic time and length scale with combined 5-nm spatial and sub-picosecond temporal resolution [3]. Real-space sensitivity to local changes of the CDW amplitude is obtained by a tailor-made dark-field mask, thus gaining insights into ultrafast dynamics induced by ultrashort laser excitation in the presence of spatial heterogeneity.

1. A. H. Zewail, Science 328, 187-193 (2010)

2. A. Feist et al., Ultramicroscopy 176, 63-73 (2017)

3. Th. Danz, T. Domröse, C. Ropers, Science 371, 371-374 (2021)