The recent discovery of high-temperature superconductivity in pressurized nickelates has renewed interest in the broken-symmetry states of their ambient-pressure parent phases, where a density wave (DW) order emerges and competes with superconductivity, but its microscopic origin remains unresolved. Using ultrafast optical spectroscopy, we track quasiparticle relaxation dynamics across the DW transition at T₃ₖ1360. 28em{0ex}K in trilayer nickelate La₄Ni₃O₁₀ single crystals, revealing the opening of an energy gap of 52 meV. Multiple coherent phonons, including A₆ modes near 3. 88, 5. 28, and 2. 09 THz, display pronounced mode-selective anomalies across the transition, indicating that the DW is strongly coupled to lattice degrees of freedom and suggesting an important role of electron-phonon coupling. At higher excitation densities, the DW is nonthermally suppressed, producing a temperature-fluence phase diagram that parallels pressure-tuned behavior. These results establish the DW in La₄Ni₃O₁₀ as a lattice-entangled instability involving multiple phonon modes, and highlight ultrafast optical excitation as a nonequilibrium tuning parameter for suppressing density wave order in nickelates.
Zhang et al. (Mon,) studied this question.