Disentangling Amplitude and Phase Dynamics in Nonequilibrium Charge Density Wave Formation

At thermal equilibrium, a broken symmetry phase characterized by a complex order parameter often develops fluctuating order with a finite amplitude above the transition temperature T_c. This is particularly pronounced in low-dimensional systems, where short-range, fluctuating order establishes its long-range phase coherence only below T_c. By using an intense laser pulse that transiently restores the high-symmetry state, we study the nonequilibrium version of such a phase transition on a prototypical charge density wave compound LaTe₃. With a combination of time-resolved diffraction, optical, and spectroscopic measurements, we can monitor how the amplitude and phase of the order parameter separately recover with distinct signatures in both coherent and incoherent responses after the photoexcitation. The present work provides a comprehensive picture on how the broken symmetry phase develops at the femto- to picosecond timescale in a low dimensional charge density wave system.