Multiferroic-Enabled Magnetic-Excitons in 2D Quantum-Entangled Van der Waals Antiferromagnet NiI<sub>2</sub>.

Son, Suhan; Lee, Youjin; Kim, Jae Ha; Kim, Beom Hyun; Kim, Chaebin; Na, Woongki; Ju, Hwiin; Park, Sudong et al. · Adv Mater · 2022

basic_science · Level V

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Abstract

Matter-light interaction is at the center of diverse research fields from quantum optics to condensed matter physics, opening new fields like laser physics. A magnetic exciton is one such rare example found in magnetic insulators. However, it is relatively rare to observe that external variables control matter-light interaction. Here, it is reported that the broken inversion symmetry of multiferroicity can act as an external knob enabling magnetic excitons in the van der Waals antiferromagnet NiI<sub>2</sub> . It is further discovered that this magnetic exciton arises from a transition between Zhang-Rice-triplet and Zhang-Rice-singlet fundamentally quantum-entangled states. This quantum entanglement produces an ultrasharp optical exciton peak at 1.384 eV with a 5 meV linewidth. The work demonstrates that NiI<sub>2</sub> is 2D magnetically ordered with an intrinsically quantum-entangled ground state.