Decoupling of static and dynamic criticality in a driven Mott insulator

TL;DR

This study reveals a unique far-from-equilibrium critical regime in a photo-doped Mott insulator where magnetic correlation length and relaxation time diverge independently, challenging traditional thermal critical behavior.

Contribution

It demonstrates the decoupling of static and dynamic criticality in a driven quantum system using advanced optical spectroscopy techniques.

Findings

Decoupled divergence of correlation length and relaxation time.

Violation of conventional thermal critical behavior.

Identification of a non-equilibrium phase diagram.

Abstract

Dynamically driven interacting quantum many-body systems have the potential to exhibit properties that defy the laws of equilibrium statistical mechanics. A widely studied model is the impulsively driven antiferromagnetic Mott insulator, which is predicted to realize exotic transient phenomena including dynamical phase transitions into thermally forbidden states and highly non-thermal magnon distributions. 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 Mott insulator Sr$_2$IrO$_4$. We uncover 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.