Dimensionality dependent electronic structure of the exfoliated van der Waals antiferromagnet NiPS$_3$

TL;DR

This study uses RIXS to reveal how the electronic structure of NiPS3 changes with layer thickness, showing a decrease in hopping integrals and charge-transfer energy, affecting magnetic interactions and order in 2D limits.

Contribution

It provides the first detailed analysis of how electronic and magnetic properties of NiPS3 evolve from bulk to few-layer forms, highlighting interlayer effects.

Findings

Decreased multiplet excitation energies with fewer layers.

Charge-transfer energy reduces from 0.60 eV (bulk) to 0.22 eV (3L).

Magnetic exchange interactions weaken with decreasing thickness.

Abstract

Resonant Inelastic X-ray Scattering (RIXS) was used to measure the local electronic structure in few-layer exfoliated flakes of the van der Waals antiferromagnet NiPS$_3$. The resulting spectra show a systematic softening and broadening of $NiS_6$ multiplet excitations with decreasing layer count from the bulk to three atomic layers (3L). These trends are driven by a decrease in the transition metal-ligand and ligand-ligand hopping integrals, and in the charge-transfer energy: $\Delta$ = 0.60 eV in the bulk and 0.22 eV in 3L NiPS$_3$. Relevant intralayer magnetic exchange integrals computed from the electronic parameters exhibit a systematic decrease in the average interaction strength with thickness and place 2D NiPS$_3$ close to the phase boundary between stripy and spiral antiferromagnetic order, which may explain the apparent vanishing of long-range order in the 2D limit. This study explicitly demonstrates the influence of $inter$layer electronic interactions on $intra$layer ones in insulating magnets. As a consequence, the magnetic Hamiltonian in few-layer insulating magnets can be significantly different from that in the bulk.