A growing list of Ce-based magnets have shown an extra and heretofore unexplained crystal electric field (CEF) mode at high energies. We describe a process whereby an optical phonon can produce a split CEF mode well above the phonon energy. We use density functional theory and point-charge model calculations to estimate the phonon distortions and coupling to model this effect in KCeO2, showing that it accounts for the extra CEF mode observed. This mechanism is generic, and may explain the extra modes observed on a variety of Ce3+ compounds.
@article{arxiv.2505.18089,
title = {Explaining the extra crystal field mode in ACeX2},
author = {Allen O. Scheie and Sabrina J. Li and Stephen D. Wilson and Daniel A. Rehn},
journal= {arXiv preprint arXiv:2505.18089},
year = {2025}
}