The evolution of the complex self energy of the 5dz2 surface state on Gd(0001) following intense optical excitation is investigated by femtosecond time-resolved photoemission. We observe an ultra- fast ( << 100 fs) broadening of the line width by three times due to e-e scattering which is followed by a subsequent decrease of the binding energy due to thermal expansion of the lattice. In addition, we resolve a periodic breathing of the band structure which originates from a coherent phonon. Its real space amplitude is estimated from the binding energy shift upon lattice displacement calculated by density functional theory.
The publication is available at link DOI: 10.1103/PhysRevLett.98.097401