Distinct Charge and Spin Recovery Dynamics in a Photoexcited Mott Insulator

Pump-probe response of the spin-orbit coupled Mott insulator Sr_{2}IrO_{4} reveals a rapid creation of low-energy optical weight and suppression of three-dimensional magnetic order on laser pumping. Postpump there is a quick reduction of the optical weight but a very slow recovery of the magnetic order-the difference is attributed to weak interlayer exchange in Sr_{2}IrO_{4} delaying the recovery of three-dimensional magnetic order. We suggest that the effect has a very different and more fundamental origin. Combining spatiotemporal mean field dynamics and Langevin dynamics on the photoexcited Mott-Hubbard insulator, we show that the timescale difference is not a dimensional effect but is intrinsic to charge dynamics versus order reconstruction in a correlated system. In two dimensions, we obtain a short, almost pump-fluence-independent timescale for charge dynamics, while recovery time of magnetic order involves domain growth and increases rapidly with fluence. Apart from addressing the iridate Mott problem, our approach can be used to analyze phase competition and spatial ordering in superconductors and charge ordered systems out of equilibrium.