Speaker
Description
Time-resolved (TR) and angle-resolved photoemission (ARPES) in extended systems is often described in terms of electrons dynamics into the conduction band. However the sample is probed into an excited state which is characterized by the same number of particle of the ground states. Such states are well described in the excitonic picture.
Here I illustrate an accurate diagrammatic approach we recently proposed [1] to calculate the TR-ARPES spectrum of systems with excitons. The diagrammatic approximation applies to the relaxed regime characterized by the presence of quasi-stationary excitons and vanishing polarization. The non-equilibrium self-energy diagrams are evaluated using excited Green’s functions. The final result is an expression for the lesser Green’s function in terms of quantities that can all be calculated in a first-principles manner. The validity of the proposed theory is illustrated in a one-dimensional model system with a direct gap. We discuss possible scenarios and highlight some universal features of the exciton peaks.
[1] E. Perfetto, D. Sangalli, A. Marini, and G. Stefanucci, Phys. Rev. B 94, 245303 (2016)
