Time-resolved ARPES signatures of pump driven normal-to-excitonic insulator transition*

We consider a ground-state band insulator turning into a nonequilibrium excitonic insulator (EI) when pumping it at sub-gap frequencies slighlty larger than the excitonic energy. The macroscopic polarization in the non-equilibrium EI phase is characterized by self-sustained oscillations with a frequency depending on the absorbed energy. We show that during the pump-driving the excitonic ARPES structure undergoes a convex-to-concave shape transition and concomitantly the system goes through a BEC-BCS crossover. Furthermore attosecond pulses shone after the pump-driving at different times t_delay generate a photocurrent which oscillates in t_delay. This phenomenon is related to the AC response of an exotic Josephson junction.