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 lambda = 800 +/- 200 meV(2) for La(1.85)Sr(0.15)CuO(4) and lambda = 400 +/- 100 meV(2) for YBa(2)Cu(3)O(6.5). These values suggest a possible fundamental role of the electron-phonon interaction in the superconducting pairing mechanism.