Electron-Phonon Coupling in High-Temperature Cuprate Superconductors Determined from Electron Relaxation Rates

We determined electronic relaxation times via pump-probe optical spectroscopy using sub-15 fs pulses for the normal state of two different cuprate superconductors. We show that the primary relaxation process is the electron-phonon interaction and extract a measure of its strength, the second moment of the Eliashberg function λ⟨ω²⟩=800±200 meV² for La1.85Sr0.15CuO₄ and λ⟨ω²⟩=400±100 meV² for YBa₂Cu₃O6.5. These values suggest a possible fundamental role of the electron-phonon interaction in the superconducting pairing mechanism.