Crystalline electric field excitations and their nonlinear splitting under magnetic fields in YbOCl

TL;DR

This study identifies and analyzes the crystalline electric field excitations in YbOCl, revealing their nonlinear splitting under magnetic fields, which advances understanding of its magnetic properties and potential quantum spin liquid behavior.

Contribution

It provides the first comprehensive Raman scattering analysis of CEF excitations in YbOCl, determining CEF parameters and wave functions, and uncovers anomalous nonlinear splitting under magnetic fields.

Findings

Identified all Raman-active phonon modes and CEF excitations in YbOCl.

Determined CEF parameters and wave functions from experimental data.

Observed anomalous nonlinear CEF splitting under magnetic fields.

Abstract

Recently reported van der Waals layered honeycomb rare-earth chalcohalides REChX (RE = rare earth, Ch = chalcogen, and X = halogen) are considered to be promising Kitaev spin liquid (KSL) candidates. The high-quality single crystals of YbOCl, a representative member of the family with an effective spin of 1/2, are available now. The crystalline electric field (CEF) excitations in a rare-earth spin system are fundamentally important for understanding both finite-temperature and ground-state magnetism, but remain unexplored in YbOCl so far. In this paper, we conduct a comprehensive Raman scattering study to unambiguously identify the CEF excitations in YbOCl and determine the CEF parameters and wave functions. Our Raman experiments further reveal the anomalous nonlinear CEF splitting under magnetic fields. We have grown single crystals of YbOCl, the nonmagnetic LuOCl, and the diluted magnetic Lu_{0.86}Yb_{0.14}OCl to make a completely comparative investigation. Polarized Raman spectra on the samples at 1.8 K allow us to clearly assign all the Raman-active phonon modes and explicitly identify the CEF excitations in YbOCl. The CEF excitations are further examined using temperature-dependent Raman measurements and careful symmetry analysis based on Raman tensors related to CEF excitations. By applying the CEF Hamiltonian to the experimentally determined CEF excitations, we extract the CEF parameters and eventually determine the CEF wave functions. The study experimentally pins down the CEF excitations in the Kitaev compound YbOCl and sets a foundation for understanding its finite-temperature magnetism and exploring the possible nontrivial spin ground state.