Two dimensional (2D) semiconductors present unique opportunities to intertwine optical and magnetic functionalities and to tune these performances through defects and dopants. Here, we integrate exciton pumping into a quantum sensing protocol on nitrogen-vacancy centers in diamond to image the optically-induced transient stray fields in few-layer, antiferromagnetic CrCl3. We discover that exciton recombination enhances the in-plane magnetization of the CrCl3 layers, with a predominant effect in the surface monolayers. Concomitantly, time-resolved photoluminescence measurements reveal that nonradiative exciton recombination intensifies in atomically thin CrCl3 with tightly localized, nearly dipole-forbidden excitons and amplified surface-to-volume ratio. Supported by experiments under controlled surface exposure and density functional theory calculations, we interpret the magnetically enhanced state to result from a defect-assisted Auger recombination that optically activates electron transfer between water vapor related surface impurities and the spin-polarized conduction band. Our work validates defect engineering as a route to enhance intrinsic magnetism in single magnetic layers and opens a novel experimental platform for studying optically-induced, transient magnetism in condensed matter systems.
@article{arxiv.2312.08476,
title = {Enhanced Magnetization by Defect-Assisted Exciton Recombination in Atomically Thin CrCl$_3$},
author = {Xin-Yue Zhang and Thomas K. M. Graham and Hyeonhu Bae and Yu-Xuan Wang and Nazar Delegan and Jonghoon Ahn and Zhi-Cheng Wang and Jakub Regner and Kenji Watanabe and Takashi Taniguchi and Minkyung Jung and Zdeněk Sofer and Fazel Tafti and David D. Awschalom and F. Joseph Heremans and Binghai Yan and Brian B. Zhou},
journal= {arXiv preprint arXiv:2312.08476},
year = {2024}
}