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Field-induced magnetic phase transition driven by a ground-state level crossing in CsErSe2

Hope Whitelock1, Allen O. Scheie2, Marissa McMaster1, Ian A. Leahy1, Li Xiang3, Mykhaylo Ozerov3, Dmitry Smirnov3, Eun Sang Choi3, C. dela Cruz4 et al.

M. O. Ajeesh2,5, Eliana S. Krakovsky6,7, Daniel A. Rehn7, Jie Xing4, Athena S. Sefat8, and Minhyea Lee1,*

  • *Contact author: minhyea.lee@colorado.edu
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Phys. Rev. Research 8, 043072 – Published 19 October, 2026

DOI: https://doi.org/10.1103/j14s-sfj5

Abstract

We report a comprehensive study of the low-temperature magnetic properties of the insulating rare-earth triangular magnet CsErSe2. We uncover a field-induced level crossing at the crystal electric field ground state, which gives rise to a first-order phase transition as well as to distinctive magnetic properties. This crossing is identified by the accurate determination of the single-ion Hamiltonian, the reliability of which is substantially enhanced by field-dependent optical spectroscopy that directly tracks the Zeeman splittings of Kramers doublets. We also observe spontaneous antiferromagnetic ordering in CsErSe2 below TN≈110mK and resolve the corresponding magnetic structure using elastic neutron scattering. We discuss how the rich magnetic behavior of CsErSe2 arises from the interplay of nontrivial field-dependent single-ion physics and spontaneous ordering, and highlight the implications of these results for understanding magnetic phenomena across a wide range of insulating rare-earth magnets.

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Phys. Rev. Research 8, 043072– Published 19 October, 2026
  • Received 12 November 2025
  • Accepted 17 September 2026
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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.

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