Time resolved photoemission on Mott insulators and High Temperature Superconductors
Jeudi 22/02/2007, 11:00
Petit Amphi, LPS Bât. 510, Orsay
We monitor the photoelectrons emitted by a Mott insulator after the absorption of an intense laser pulse. This experiment allows us to visualize directly the ultrafast breakdown of the insulating phase and the coherent excitation of a coupled phonon mode. The Mott phase is fully restored after 1 ps but a coherently excited phonon induces electronic oscillations lasting longer than 20 ps. As a consequence, the effects of electron-electron and electron-phonon interactions can be clearly disentangled. Time resolved photoemission is also employed to investigate optimally doped Bi2Sr2CaCu2O8. Two stages characterize the cooling dynamics: hot electrons emit non-equilibrium phonons with characteristic time of 110 fs, whereas hot phonons decay with time constant of 2 ps. The unusual relaxation of electronic energy is ascribed to the strong anisotropy of the electron-phonon interaction. A quantitative evaluation of interaction strength shows that electron-phonon coupling is too weak to explain high temperature superconductivity.