Direct Observation and Analysis of Low-Energy Magnons with Raman Spectroscopy in Atomically Thin NiPS3

TL;DR

This paper demonstrates that Raman spectroscopy can directly observe low-energy magnons in atomically thin NiPS3, providing high energy resolution and insights into spin-exchange interactions, advancing the study of 2D magnetic materials.

Contribution

It introduces Raman spectroscopy as a powerful tool for probing low-energy spin dynamics in atomically thin vdW magnets, revealing hidden information about spin-exchange paths.

Findings

Raman spectroscopy detects low-energy magnons (~1 meV) in bilayer NiPS3.

Polarization dependence reveals spin-exchange interaction details.

Confirmed magnon origin through comparison with neutron scattering data.

Abstract

Van der Waals (vdW) magnets have rapidly emerged as a fertile playground for novel fundamental physics and exciting applications. Despite the impressive developments over the past few years, technical limitations pose a severe challenge to many other potential breakthroughs. High on the list is the lack of suitable experimental tools for studying spin dynamics on atomically thin samples. Here, Raman scattering techniques are employed to observe directly the low-lying magnon (~1 meV) even in bilayer NiPS3. The unique advantage is that it offers excellent energy resolutions far better on low-energy sides than most inelastic neutron spectrometers can offer. More importantly, with appropriate theoretical analysis, the polarization dependence of the Raman scattering by those low-lying magnons also provides otherwise hidden information on the dominant spin-exchange scattering paths for different magnons. By comparing with high-resolution inelastic neutron scattering data, these low-energy Raman modes are confirmed to be indeed of magnon origin. Because of the different scattering mechanisms involved in inelastic neutron and Raman scattering, this new information is fundamental in pinning down the final spin Hamiltonian. This work demonstrates the capability of Raman spectroscopy to probe the genuine two-dimensional spin dynamics in atomically-thin vdW magnets, which can provide novel insights that are obscured in bulk spin dynamics.