Out-of-equilibrium phase competition mediated by photoinduced fluctuations

Engineering novel states of matter by an ultrafast laser pulse is at the forefront of materials research. One promising approach relies on systems that host competing ground states, where light suppresses the dominant order in equilibrium while strengthening the subdominant one. However, the interplay among competing orders remains difficult to study due to a lack of experimental probes that can measure intertwined dynamics all at once. In this talk, I will discuss a model charge-density-wave (CDW) family with two competing modulations, out of which only the dominant one appears in equilibrium. Using a pump-pump-probe scheme with ultrafast electron diffraction, we find that both CDW orders emerge simultaneously after photoexcitation. This joint growth lasts for a few picoseconds and features fluctuating patches of both density waves – in striking resemblance to the critical state near the equilibrium transition temperature. Our investigation unveils a codeveloping relation between an otherwise incompatible pair of CDWs in equilibrium. It further establishes photoinduced fluctuations as a generic pathway for realizing transient states in solids that possess competing phases.