Ultrafast dynamics evidence of strong coupling superconductivity in LaH_10±δ

Recently, tremendous research interest has been aroused in clathrate superhydrides. However, their microscopic properties, especially the superconducting (SC) gap and electron-phonon coupling (EPC) strength, are largely unexplored experimentally. Here, we investigate the time-resolved ultrafast spectroscopy of a superconductor LaH_10±δ under an ultrahigh pressure of 165 GPa. By analyzing the ultrafast dynamics of the quasiparticles, we experimentally obtain the SC gap Δ(0) = 53 ± 5 meV, revealing a gap ratio 2Δ(0)/k_BT_c = 5.6 and a gap parameter ϑ = 1.95. Significantly, we experimentally estimate \(\lambda \langle {\Omega }^{2}\rangle\) $\lambda ⟨{\mathrm{\Omega }}^2⟩$  = (2.4 ± 0.1) × 10⁴ (meV)², which corresponds to an EPC strength λ = 2.58 ± 0.11. These results together provide direct experimental evidence that strong EPC is responsible for the near-room-temperature superconductivity in clathrate superhydrides. Our investigation significantly advances the experimental exploration of superhydrides, and contributes to the ultrafast dynamics investigations of quantum materials under high pressures.