Time resolved photoelectron spectroscopy is employed to study the dynamics of photoexcited electrons in optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212). Hot electrons thermalize in less than 50 fs and dissipate their energy in two steps. The cooling of the electronic temperature on two distinct timescales (110 fs and 2 ps, respectively) is attributed to the generation and subsequent decay of non-equilibrium phonons. We conclude that most of the electron-phonon interaction is due to 20% of the total lattice modes. A simple modeling accounts for the two cooling steps of the electrons and provides an estimates of the second momentum of the Eliashberg coupling function. The resulting value λΩ2 = 360 ± 30 meV2 sets an upper limit λ = 0:22 to the average electron-phonon coupling..
The publication is available at link DOI: 10.1103/PhysRevLett.99.197001