Orbital-selective Time-Domain Signature of Nematicity Dynamics in the Charge-Density-wave Phase of La_1.65Eu_0.2Sr_0.15CuO_4

Understanding the interplay between charge, nematic, and structural orderingtendencies in cuprate superconductors is critical to unraveling their complexphase diagram. Using pump-probe time-resolved resonant x-ray scattering on the(0 0 1) Bragg peak at the Cu L_3 and O K resonances, we investigatenon-equilibrium dynamics of Q_a = Q_b = 0 nematic order and its associationwith both charge density wave (CDW) order and lattice dynamics inLa_1.65Eu_0.2Sr_0.15CuO_4. The orbital selectivity of theresonant x-ray scattering cross-section allows nematicity dynamics associatedwith the planar O 2p and Cu 3d states to be distinguished from the responseof anisotropic lattice distortions. A direct time-domain comparison of CDWtranslational-symmetry breaking and nematic rotational-symmetry breakingreveals that these broken symmetries remain closely linked in the photoexcitedstate, consistent with the stability of CDW topological defects in theinvestigated pump fluence regime.