Crystal Anisotropy Implications on the Magneto-Optical Properties of van der Waals FePS3

TL;DR

This study demonstrates how in-plane structural anisotropy in FePS3 influences its optical responses and polarization behaviors, with implications for spintronic device applications.

Contribution

It reveals the direct relationship between lattice anisotropy, electronic transitions, and optical properties in FePS3 from bulk to monolayer.

Findings

Four distinct emission bands identified with different polarization behaviors.

Density functional theory explains the electronic structure and polarization responses.

Structural anisotropy significantly affects optical responses in FePS3.

Abstract

Antiferromagnetic FePS3 has recently gained significant interest in its potential applications in spin-related devices. Here, we show that in-plane structural anisotropy has a major impact in shaping the optical responses of FePS3 single-crystals from the bulk form down to the monolayer limit. X-ray diffraction on a bulk FePS3 crystal confirms a distorted FeS6 octahedron causing inequivalent Fe-Fe distances and consequently resulting in a higher a/b lattice parameter ratio. Micro-photoluminescence observations on bulk and monolayer FePS3 reveal four emissions: one intra-atomic d-d transition (band A, centered at ~1.24 eV) and three p-d charge transfer transitions (bands B, C, and D, centered around ~1.79 eV, ~2.3 eV, and ~2.56 eV, respectively). These bands exhibit different polarization behaviors, which persist down to the monolayer limit. Density functional theory calculations from bulk to monolayer FePS3 reveal the underlying electronic structure, assign the observed emissions, and indicate why these peaks have contrasting linear and circular polarization responses. These results establish a direct structure-optics relation in FePS3, highlighting the strong coupling between lattice anisotropy, electronic transitions, and symmetry-selective optical selection rules.