Energy scales in 4f1 delafossite magnets: crystal-field splittings larger than the strength of spin-orbit coupling in KCeO2

TL;DR

This study investigates KCeO2, revealing unusually large crystal-field splittings that influence its magnetic properties and making it a valuable model for understanding spin-orbit coupling effects in 4f quantum magnets.

Contribution

The paper provides detailed theoretical analysis showing large crystal-field splittings in KCeO2, highlighting their impact on magnetic anisotropy and ground-state properties.

Findings

Large crystal-field splittings up to 320 meV predicted

KCeO2 is in the strong field coupling regime

Interplay between ligand electrostatics and trigonal field identified

Abstract

Ytterbium-based delafossites with effective S=1/2 moments are investigated intensively as candidates for quantum spin-liquid ground states. While the synthesis of related cerium compounds has also been reported,many important details concerning their crystal, electronic, and magnetic structures are unclear. Here we analyze the S=1/2 system KCeO2, combining complementary theoretical methods. The lattice geometry was optimized and the band structure investigated using density functional theory extended to the level of a GGA+U calculation in order to reproduce the correct insulating behavior. The Ce 4f1 states were then analyzed in more detail with the help of ab initio wave-function-based computations. Unusually large effective crystal-field splittings of up to 320 meV are predicted, which puts KCeO2 in the strong field coupling regime. Our results reveal a subtle interplay between ligand-cage electrostatics and the trigonal field generated by the extended crystalline surroundings, relevant in the context of recent studies on tuning the nature of the ground-state wave function in 4f triangular-lattice and pyrochlore compounds. It also makes KCeO2 an interesting model system in relation to the effect of large crystal-field splittings on the anisotropy of intersite exchange in spin-orbit coupled quantum magnets.