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Trigonal distortion in the Kitaev candidate honeycomb magnet ${BaCo}_{2} ({AsO}_{4})_{2}$

M. M. Ferreira-Carvalho ^1,2, S. Rößler ¹, C. F. Chang ¹, Z. Hu¹, S. M. Valvidares³, P. Gargiani ³, M. W. Haverkort⁴, Prashanta K. Mukharjee ⁵, P. Gegenwart ⁵ et al.

A. A. Tsirlin ⁶ and L. H. Tjeng ¹

¹Max Planck Institute for Chemical Physics of Solids, Nöthnitzer Str. 40, 01187 Dresden, Germany
²Institute of Physics II, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
³ALBA Synchrotron Light Source, E-08290 Cerdanyola del Vallès, Barcelona, Spain
⁴Institute for Theoretical Physics, Heidelberg University, Philosophenweg 19, 69120 Heidelberg, Germany
⁵Experimental Physics VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, 86159 Augsburg, Germany
⁶Felix Bloch Institute for Solid-State Physics, University of Leipzig, 04103 Leipzig, Germany

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Phys. Rev. B 112, 125135 – Published 16 September, 2025

DOI: https://doi.org/10.1103/2sdd-pyx1

Abstract

We conducted x-ray absorption (XAS) and magnetic circular dichroism (XMCD) measurements at the Co $L_{2, 3}$ edges on single crystals of the Kitaev candidate honeycomb lattice compound ${BaCo}_{2} {({AsO}_{4})}_{2}$ . The measurements employed the inverse partial fluorescence yield technique, which is ideal for acquiring reliable x-ray absorption spectra from highly insulating samples, enabling precise quantitative analysis. Our experimental results revealed a significant linear dichroic signal, indicating strong trigonal distortion in the ${CoO}_{6}$ octahedra in ${BaCo}_{2} {({AsO}_{4})}_{2}$ . We performed a detailed analysis of the experimental XAS and XMCD spectra using a full-multiplet configuration-interaction cluster model. This analysis unveiled that the $t_{2 g}$ hole density is predominantly localized in the $a_{1 g}$ orbital. Through XMCD sum rules and theoretical calculations, we quantified both the spin and orbital magnetic moments. Our study demonstrates that the local electronic structure of the ${CoO}_{6}$ octahedra displays an effective trigonal distortion of approximately $- 0.114$ eV. This distortion is larger than the Co $3 d$ spin-orbit coupling constant, emphasizing the crucial impact of local structural distortions on the electronic and magnetic properties of ${BaCo}_{2} {({AsO}_{4})}_{2}$ .

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Phys. Rev. B 112, 125135– Published 16 September, 2025

Vol. 112, Iss. 12 — 15 September 2025

Received 22 May 2025
Revised 15 August 2025
Accepted 28 August 2025

DOI: https://doi.org/10.1103/2sdd-pyx1

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by Max Planck Society.

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Trigonal distortion in the Kitaev candidate honeycomb magnet ${BaCo}_{2} ({AsO}_{4})_{2}$

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Trigonal distortion in the Kitaev candidate honeycomb magnet BaCo2(AsO4)2

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References (54)

Trigonal distortion in the Kitaev candidate honeycomb magnet ${BaCo}_{2} ({AsO}_{4})_{2}$