Trigonal Distortion Driven Ground States in VX3 (X = Br and I)

TL;DR

This study uses advanced spectroscopic techniques and calculations to elucidate the electronic ground states of V$X_3$ compounds, revealing how trigonal distortion influences their magnetic properties.

Contribution

It provides the first detailed experimental determination of the low energy electronic structure and trigonal distortion effects in V$X_3$ (X=Br, I), informing 2D magnetic material design.

Findings

Trigonal distortion parameters differ in VBr$_3$ and VI$_3$, indicating opposite signs.

High-spin V$^{3+}$ configuration with specific ground states was confirmed.

Variation in covalency from Br to I was observed through electronic structure parameters.

Abstract

Transition-metal halides V$X_3$ ($X$ = Br and I) have emerged as promising candidates for two dimensional spintronic and quantum applications due to their layer-dependent magnetism and tunable electronic states. However, experimental insights into their ground state electronic structures remain limited. Here, we present a comprehensive investigation of V$X_3$ using high resolution resonant inelastic x-ray scattering (RIXS) combined with ligand field multiplet calculations. The RIXS spectra reveal distinct $dd$ and charge-transfer excitations, allowing precise determination of electronic structure parameters, including the crystal field splitting, trigonal distortion, and Racah parameters. The determined parameters showed clear variation, indicating an increase in covalency from Br to I. The trigonal distortion parameters $\Delta_{D_{3d}}$ were determined to be -0.096 eV in VBr$_3$ and 0.07 eV in VI$_3$, indicating a sign opposition between the two compounds, reflecting good agreement with experimental RIXS data. Cluster model calculations yield a high-spin V$^{3+}$ $(S = 1)$ configuration, with an $e'^2_g$ ground state in VBr$_3$ and an $e'^1_ga^1_{1g}$ ground state in VI$_3$, consistent with trigonal elongation and compression, respectively. Our findings provide the most complete experimental determination of the low energy electronic structure in V$X_3$, offering valuable insights for designing 2D magnetic and spintronic materials based on vanadium halides.