Exciton-driven antiferromagnetic metal in a correlated van der Waals insulator

TL;DR

This paper reports the discovery of a transient metallic state with antiferromagnetic order in a correlated van der Waals insulator, driven by photoexcited excitons, revealing new possibilities for optical control of magnetism.

Contribution

It demonstrates the creation of a transient antiferromagnetic metal phase via exciton excitation in NiPS₃, a novel phenomenon in correlated van der Waals materials.

Findings

Observation of coexistence of itinerant carriers and antiferromagnetic magnons

Detection of a transient metallic state with preserved antiferromagnetism

Evidence of exciton-driven optical manipulation of magnetic phases

Abstract

Collective excitations of bound electron-hole pairs -- known as excitons -- are ubiquitous in condensed matter, emerging in systems as diverse as band semiconductors, molecular crystals, and proteins. Recently, their existence in strongly correlated electron materials has attracted increasing interest due to the excitons' unique coupling to spin and orbital degrees of freedom. The non-equilibrium driving of such dressed quasiparticles offers a promising platform for realizing unconventional many-body phenomena and phases beyond thermodynamic equilibrium. Here, we achieve this in the van der Waals correlated insulator NiPS$_3$ by photoexciting its newly discovered spin-orbit-entangled excitons that arise from Zhang-Rice states. By monitoring the time evolution of the terahertz conductivity, we observe the coexistence of itinerant carriers produced by exciton dissociation and the long-wavelength antiferromagnetic magnon that coherently precesses in time. These results demonstrate the emergence of a transient metallic state that preserves long-range antiferromagnetism, a phase that cannot be reached by simply tuning the temperature. More broadly, our findings open an avenue toward the exciton-mediated optical manipulation of magnetism.