Coherence and de-coherence in the Time-Resolved ARPES of realistic materials: An ab-initio perspective.

Coherence and de-coherence are the most fundamental steps that follow the initial photo-excitation occurring in typical pump-and-probe experiments. Indeed, the initial external laser pulse transfers coherence to the system in terms of creation of multiple electron–hole pairs excitation. The excitation concurs both to the creation of a finite carriers density and to the appearance of induced electromagnetic fields. The two effects, to a very first approximation, can be connected to the simple concepts of populations and oscillations. The dynamics of the system following the initial photo-excitation is, thus, entirely dictated by the interplay between coherence and de-coherence. This interplay and the de-coherence process itself, is due to the correlation effects stimulated by the photo-excitation. Single-particle, like the electron–phonon, and two-particles, like the electron–electron, scattering processes induce a complex dynamics of the electrons that, in turn, makes the description of the correlated and photo-excited system in terms of pure excitonic and/or carriers populations challenging. • In any Pump-Probe experiment the driving field transfers coherence to the system • After photo-excitation a complex interplay of coherence and decoherence takes place. • Time-Resolved ARPES is a powerful tool to access the nonequilibrium carrier dynamics • Time-Resolved ARPES provides a sharp evidence of the role played by excitonic effects • Time-Resolved Angle Resolved Spectroscopy is a powerful tool to access the out-of-equilibrium carrier dynamics and can provide a sharp evidence of the role played by excitonic effects. [ABSTRACT FROM AUTHOR]