Separating terahertz spin and charge contributions from ultrathin antiferromagnetic heterostructures

TL;DR

This study introduces a novel method combining high magnetic fields and symmetry analysis to distinguish spin and charge contributions in terahertz emission from ultrathin antiferromagnetic heterostructures, clarifying emission mechanisms.

Contribution

The paper presents an unprecedented methodology to separate spin and charge contributions in terahertz emission, resolving debates and advancing terahertz spintronics research.

Findings

Identified two mechanisms: optical difference frequency generation and ultrafast magnetization quenching.

No evidence of spin transport effects or coherent magnons in the emission.

Method applicable to various magnetically ordered heterostructures.

Abstract

Femtosecond laser excitation of nanometer thin heterostructures comprising a heavy metal and a magnetically ordered material is known to result in the emission of terahertz radiation. However, the nature of the emitted radiation from heavy metal~/~antiferromagnet heterostructures has sparked debates and controversies in the literature. Here, we unambiguously separate spin and charge contributions from Pt~/~NiO heterostructures by introducing an unprecedented methodology combining high external magnetic fields with a symmetry analysis of the emitted terahertz polarization. We observe two distinct mechanisms of terahertz emission which we identify as optical difference frequency generation and ultrafast laser-induced quenching of the magnetization. We emphasize the absence of spin transport effects and signatures of coherent magnons. Overall, our work provides a general experimental methodology to separate spin and charge contributions to the laser-induced terahertz emission from heterostructures comprising a magnetically ordered material thus holding great potential for advancing terahertz spintronics and establishing terahertz orbitronics.