Long-lived population inversion in resonantly driven excitonic antiferromagnet

TL;DR

This paper reports the discovery of a long-lived, photo-induced population inversion state in the van der Waals antiferromagnet NiPS3, which could enable terahertz lasing in two-dimensional materials.

Contribution

It reveals a resonantly driven, long-lived population inversion in NiPS3, a novel state with potential applications in terahertz laser technology.

Findings

Long-lived 17 ps population inversion state observed

Negative photoconductivity indicates population inversion

Resonant pumping at 1.476 eV is essential for state creation

Abstract

Van der Waals magnets are an emerging material family for investigating light-matter interactions and spin-correlated excitations. Here, we report the discovery of a photo-induced state with a lifetime of 17 ps in the van der Waals antiferromagnet NiPS$_3$, which appears exclusively with resonant pumping at 1.476 eV in the antiferromagnetic state. The long-lived state comes with a negative photoconductivity, a characteristic optical response of population inversion. Our findings demonstrate a promising pathway to potentially achieve long-lived lasing at terahertz frequencies in reduced dimensions.