Keldysh space control of charge dynamics in a strongly driven Mott insulator*

The fate of a Mott insulator under strong low frequency optical driving conditions is a fundamental problem in quantum many-body dynamics. Using ultrafast broadband reflectivity spectroscopy and second-harmonic generation rotational anisotropy experiments, we measured the transient out-of-equilibrium doublon-holon and electronic structure dynamics of an off resonantly pumped Mott insulator Ca₂RuO₄. We observed coherent bandwidth renormalization and nonlinear doublon-holon pair production occurring in rapid succession within a sub-100 femtosecond pump pulse duration. By sweeping the off-resonant electric field amplitude, we demonstrate continuous bandwidth tuning and a Keldysh cross-over from a multi-photon absorption to quantum tunneling dominated pair production regime. The time dynamics of antiferromagnetic order under the impact of nonlinear pair production was investigated. Our results provide a procedure to control coherent and nonlinear heating processes in Mott insulators, facilitating the discovery of novel out-of-equilibrium phenomena in strongly correlated systems.