  In the past decade, the advent of time-resolved spectroscopic tools has
provided a new ground to explore fundamental interactions in solids and to
disentangle degrees of freedom whose coupling leads to broad structures in the
frequency domain. Time- and angle-resolved photoemission spectroscopy
(tr-ARPES) has been utilized to directly study the relaxation dynamics of a
metal in the presence of electron-phonon coupling. The effect of
photo-excitations on the real and imaginary part of the self-energy as well as
the time scale associated with different recombination processes are discussed.
In contrast to a theoretical model, the phonon energy does not set a clear
scale governing quasiparticle dynamics, which is also different from the
results observed in a superconducting material. These results point to the need
for a more complete theoretical framework to understand electron-phonon
interaction in a photo-excited state.
