Femtosecond electron imaging of a transformation between different symmetry broken ground states of 2D charge density wave near a nonthermal critical point*

We study the atomic scale dynamics of a CDW phase transition from a stripe phase into a new topological phase in rare-earth tritelluride compound. Such a new state is a hidden ground state not allowed thermodynamically, but is driven to form after an interaction quench by an intense infrared laser pulse. With femtosecond electron-based scattering, we capture the entire course of this transformation and show an emergent self-organization that defines a nonthermal critical point substantially different from a thermal critical point. The dynamical stabilization after the quench is achieved through the inherent underpinning symmetry that allows the development of the long-range coherence simultaneously for different broken symmetry states at far from equilibrium.