Decoupling of static and dynamic criticality in a driven Mott insulator

Strongly driven antiferromagnetic Mott insulators have the potential to exhibit exotic transient phenomena that are forbidden in thermal equilibrium. However, such far-from-equilibrium regimes, where conventional time-dependent Ginzburg-Landau descriptions fail, are experimentally challenging to prepare and to probe especially in solid state systems. Here we use a combination of time-resolved second harmonic optical polarimetry and coherent magnon spectroscopy to interrogate n -type photo-doping induced ultrafast magnetic order parameter dynamics in the antiferromagnetic Mott insulator Sr 2 IrO 4 . We find signatures of an unusual far-from-equilibrium critical regime in which the divergences of the magnetic correlation length and relaxation time are decoupled. This violation of conventional thermal critical behavior arises from the interplay of photo-doping and non-thermal magnon population induced demagnetization effects. Our findings, embodied in a non-equilibrium phase diagram, provide a blueprint for engineering the out-of-equilibrium properties of quantum matter, with potential applications to terahertz spintronics technologies. The impulsively driven antiferromagnetic Mott insulator is a model quantum many-body system predicted to realize exotic transient phenomena, however its exploration in far-from equilibrium regimes remains experimentally challenging. Here, the authors use a combination of second harmonic optical polarimetry and coherent magnon spectroscopy to investigate the ultrafast non-equilibrium dynamics of the Mott insulator Sr 2 IrO 4 and find evidence of a far-from-equilibrium critical regime where static and dynamic critical behaviour decouple and which could be present in a number of other quantum materials.