Observation of excitons bound by antiferromagnetic correlations

TL;DR

This study provides experimental evidence that excitons in two-dimensional Mott insulators are bound by antiferromagnetic correlations, with stability linked to magnetic order and robustness against screening, opening new avenues for magnetic control of excitons.

Contribution

First experimental confirmation that antiferromagnetic correlations can bind excitons in 2D Mott insulators, demonstrating their stability and potential for magnetic manipulation.

Findings

Excitons only exist below the temperature where AFM correlations develop.

Excitons remain stable up to high photodoping densities near the Mott transition.

Results confirm spin-mediated exciton binding in 2D Mott insulators.

Abstract

Two-dimensional Mott insulators host antiferromagnetic (AFM) correlations that are predicted to enhance the attractive interaction between empty (holons) and doubly occupied (doublons) sites, creating a novel pathway for exciton formation. However, experimental confirmation of this spin-mediated binding mechanism remains elusive. Leveraging the distinct magnetic critical properties of the Mott antiferromagnets Sr$_2$IrO$_4$ and Sr$_3$Ir$_2$O$_7$, we show using time-resolved THz spectroscopy that excitons only exist at temperatures below where short-range AFM correlation develops. The excitons remain stable up to photodoping densities approaching the predicted excitonic Mott insulator-to-metal transition, revealing a unique robustness against screening. Our results establish the viability of spin-bound excitons and introduce opportunities for excitonic control through magnetic degrees of freedom.