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 optical spectroscopy, we measured the transient electronic
structure and charge dynamics of an off-resonantly pumped Mott insulator
Ca2​RuO4​. We observe coherent bandwidth renormalization and nonlinear
doublon-holon pair production occurring in rapid succession within a sub-100
femtosecond pump pulse duration. By sweeping the 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.
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.Comment: 6 pages main text, 4 figures, 16 pages supplementary informatio