Spectroscopy of the frustrated quantum antiferromagnet Cs$_2$CuCl$_4$

TL;DR

This study combines RIXS and DFT to analyze the electronic structure of Cs$_2$CuCl$_4$, revealing crystal field parameters and orbital excitations, advancing understanding of frustrated quantum antiferromagnets.

Contribution

It demonstrates the effectiveness of integrating RIXS, DFT, and crystal field theory to accurately determine electronic ground states in complex magnetic materials.

Findings

Resolved crystal field splitting parameters D_q, D_s, D_τ

Assigned dd orbital excitations in Cs$_2$CuCl$_4$

Validated ab-initio electronic structure with experimental spectra

Abstract

We investigate the electronic structure of Cs$_2$CuCl$_4$, a material discussed in the framework of a frustrated quantum antiferromagnet, by means of resonant inelastic x-ray scattering (RIXS) and Density Functional Theory (DFT). From the non-dispersive highly localized dd excitations, we resolve the crystal field splitting of the Cu$^{2+}$ ions in a strongly distorted tetrahedral coordination. This allows us to model the RIXS spectrum within the Crystal Field Theory (CFT), assign the dd orbital excitations and retrieve experimentally the values of the crystal field splitting parameters D$_q$, D$_s$ and D$_{\tau}$. The electronic structure obtained ab-initio agrees with the RIXS spectrum and modelled by CFT, highlighting the potential of combined spectroscopic, cluster and DFT calculations to determine the electronic ground state of complex materials.