We investigate the crystal electric field (CEF) excitations of Yb3+ ions in powder samples of the triangular-lattice rare-earth-based antiferromagnet YbZn2GaO5 using inelastic neutron scattering (INS). Three CEF excitations from the ground-state Kramers doublet were observed, each exhibiting significant broadening beyond instrumental resolution. Combining temperature-dependent INS and neutron powder diffraction, we identify a significant static contribution to this broadening and attribute it to heterogeneous coordination of Yb3+ ions due to Ga3+/Zn2+ site mixing. Rietveld refinement of neutron powder diffraction indicates that 35% of Ga occupies the Zn site and 60% of Zn occupies the Ga site. We show with a point charge model for the CEF Hamiltonian that heterogeneous coordination of Yb3+ ions leads to broadened CEF peaks. First-principles calculations demonstrate that the random Ga3+/Zn2+ distribution can produce the distortions of the YbO6 octahedra observed from neutron diffraction. Because the documented heterogeneity will extend to exchange interactions, our results suggest that disorder is a significant factor in the unusual magnetism previously reported in YbZn2GaO5, including broad low-energy magnetic excitations and the absence of magnetic ordering down to 0.3K.
@article{arxiv.2507.12592,
title = {Quenched Disorder in the Triangular Lattice Antiferromagnet YbZn$_2$GaO$_5$},
author = {Leshan Zhao and Tong Chen and Matthew B. Stone and Qiang Zhang and Colin L. Sarkis and S. M. Koohpayeh and Collin Broholm},
journal= {arXiv preprint arXiv:2507.12592},
year = {2025}
}