Nonequilibrium dynamics of $\alpha$-RuCl$_{3}$ -- a time-resolved magneto-optical spectroscopy study

TL;DR

This study uses time-resolved magneto-optical spectroscopy to explore the ultrafast nonequilibrium magnetic dynamics of $ ext{RuCl}_3$, revealing slow demagnetization and long-lived spin-disordered states linked to charge excitations and phase transitions.

Contribution

It provides new insights into the ultrafast magnetic response and phase dynamics of $ ext{RuCl}_3$ after photoexcitation, highlighting the interplay of charge and spin in a Kitaev candidate.

Findings

Slow initial demagnetization occurs within tens of picoseconds.

Long-lived non-thermal spin-disordered states persist for hundreds to thousands of picoseconds.

Universal recovery dynamics suggest domain growth and propagation on nanosecond scales.

Abstract

We present time-resolved magneto-optical spectroscopy on the magnetic Mott-Hubbard-insulating Kitaev spin liquid candidate $\alpha$-RuCl$_3$ to investigate the nonequilibrium dynamics of its antiferromagnetically ordered zigzag groundstate after photoexcitation. A systematic study of the transient magnetic linear dichroism under different experimental conditions (temperature, external magnetic field, photoexcitation density) gives direct access to the dynamical interplay of charge excitations with the zigzag ordered state on ultrashort time scales. We observe a rather slow initial demagnetization (few to 10s of ps) followed by a long-lived non-thermal antiferromagnetic spin-disordered state (100$-$1000s of ps), which can be understood in terms of holons and doublons disordering the antiferromagnetic background after photoexcitation. Varying temperature and fluence in the presence of an external magnetic field reveals two distinct photoinduced dynamics associated with the zigzag and quantum paramagnetic disordered phases. The photo-induced non-thermal spin-disordered state shows universal compressed-exponential recovery dynamics related to the growth and propagation of zigzag domains on nanosecond time scales, which is interpreted within the framework of the Fatuzzo-Labrune model for magnetization reversal. The study of nonequilibrium states in strongly correlated materials is a relatively unexplored topic, but our results are expected to be extendable to a large class of Mott-Hubbard insulator materials with strong spin-orbit coupling.