The emergence of d-wave superconductivity from the Mott insulating state in the cuprates is widely understood to result from the action of strong electron-electron interactions. Nevertheless, the parallel role of the electron-phonon interaction in defining the cuprate phase-diagram is highlighted by the ubiquitous presence of charge-density-wave correlations in these materials. Although non-equilibrium studies have reported the observation of a transient superconducting state generated in response to the resonant pumping of select phonon modes [1], relatively little is understood about the dynamic properties of the electron-phonon interaction itself. Using time-resolved resonant x-ray scattering from La_1.65Eu_0.2Sr_0.15CuO₄ we studied the dynamic evolution of charge-density-wave order in response to ultrafast optical excitation, as a function of temperature and excitation fluence [2]. In a follow-up investigation, we have now tracked the corresponding structural dynamics across a wide doping range in both La_1.6-xNd_0.4Sr_xCuO₄ and La_1.8-xEu_0.2Sr_xCuO₄. By resolving the dynamics of the low-temperature tetragonal lattice distortion following femtosecond optical excitation, we isolate a channel for the flow of energy between the electronic and lattice subsystems. We find that the energy transfer rate through this channel, and hence the e-ph coupling strength, is sharply enhanced in the presence of charge-density-wave (CDW) correlations, evidenced by a dramatic reduction in the structural response time. Crucially, we demonstrate that this enhanced coupling can be dynamically suppressed on ultrafast timescales by exciting the electronic system above the CDW melting threshold, without significantly heating the lattice. These results highlight the role of electronic correlations in defining the e-ph interaction, and reveal a pathway to ultrafast control of the e-ph interaction in correlated materials.

[1] D. Fausti et al. Science 331, 189–191 (2011).

[2] M. Bluschke, N. Gupta et al. PNAS 121, e2400727121 (2024).