The origin of exciton mass in a frustrated Mott insulator Na$_2$IrO$_3$

TL;DR

This study uses ultrafast optical spectroscopy to investigate exciton relaxation in the frustrated Mott insulator Na$_2$IrO$_3$, revealing that exciton mass is primarily influenced by interactions with surrounding spins.

Contribution

It introduces a method to independently generate and analyze excitons in Na$_2$IrO$_3$, elucidating the role of spin interactions in exciton mass determination.

Findings

Exciton dynamics differ between magnetic and disordered phases.

Exciton mass is mainly affected by spin interactions.

Ultrafast spectroscopy effectively probes quasiparticle relaxation.

Abstract

We use a three-pulse ultrafast optical spectroscopy to study the relaxation processes in a frustrated Mott insulator Na$_2$IrO$_3$. By being able to independently produce the out-of-equilibrium bound states (excitons) of doublons and holons with the first pulse and suppress the underlying antiferromagnetic order with the second one, we were able to elucidate the relaxation mechanism of quasiparticles in this system. By observing the difference in the exciton dynamics in the magnetically ordered and disordered phases we found that the mass of this quasiparticle is mostly determined by its interaction with the surrounding spins.