Fig. 1. Phase competition and CDW superlattice dynamics in CsV₃Sb₅.

a, b Lattice distortions corresponding to the instabilities of phonons at M (0.5 0 0) and L (0.5 0 0.5) points in the momentum space. M00 (L00) corresponds to the case where the in-plane unit-cell doubling is along the a-axis and no doubling is present along the other two symmetry-equivalent directions, namely the b- and (a + b)-axes. c, d Two most probable 2 × 2 × 2 CDW structures of CsV₃Sb₅. Note that in panels (a–d) only the contracted bonds are colored in brown and only the V atoms are represented by the green balls for clarity. e Schematic evolution of the two competing phases, Δ₁ and Δ₂, in the phase space. The purple (green) arrow characterizes the change in the amplitude of Δ₁₍₂₎, which is suppressed less (more) by light. Two insets show that phase competition leads to a suppression in order parameter amplitude and a change in real space domain size upon light excitation. f Schematic of the near-infrared (NIR) pump and hard X-ray probe experimental setup (Methods). Time delay t between the pump and probe can be varied. The sample is rotated nearly around its surface normal to fulfill the Bragg condition for a given diffraction peak. V atoms are represented by green balls while Sb atoms are represented by purple balls. Cs atoms are neglected in the crystal structure for clarity. Raw image of the (0 -1.5 2.5) superlattice peak before pumping is shown. The inset depicts the two-dimensional X-ray camera plane in the three-dimensional momentum space when measuring the peak at (0 -1.5 2.5). The two directions, q_⊥ and q_//, are nearly parallel to L and K directions, respectively. This holds true for the other peaks under investigation. g–i Intensity linecuts I integrated over the q_// direction normalized by its equilibrium peak value at representative time delays. Solid lines are fits to Gaussians. Gray curves in panels (h, i) are the fitting curves reproduced from panel (g) for better comparison.