Field-induced magnetic phase transition driven by a ground state level-crossing in CsErSe$_2$

Hope Whitelock; Allen O. Scheie; Marissa McMaster; Ian A. Leahy; Li Xiang; Mykhaylo Ozerov; Dmitry Smirnov; Eun Sang Choi; C. dela Cruz; M. O. Ajeesh; Eliana S. Krakovsky; Daniel A. Rehn; Jie Xing; Athena S. Sefat; Minhyea Lee

arXiv · 2510.21616

Field-induced magnetic phase transition driven by a ground state level-crossing in CsErSe$_2$

Hope Whitelock·Allen O. Scheie·Marissa McMaster·Ian A. Leahy·Li Xiang·Mykhaylo Ozerov·Dmitry Smirnov·Eun Sang Choi·C. dela Cruz·M. O. Ajeesh·Eliana S. Krakovsky·Daniel A. Rehn·Jie Xing·Athena S. Sefat·Minhyea Lee

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Abstract

We report a comprehensive study of the low-temperature magnetic properties of the insulating rare-earth triangular magnet CsErSe$_2$. We uncover a field-induced level crossing at the crystal electric field (CEF) 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 CsErSe$_2$ below $T_N \approx 110$ mK, and resolve the corresponding magnetic structure using elastic neutron scattering. We discuss how the rich magnetic behavior of CsErSe$_2$ arises from the interplay of non-trivial 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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Hope Whitelock, Allen O. Scheie, Marissa McMaster, Ian A. Leahy, Li Xiang, Mykhaylo Ozerov, Dmitry Smirnov, Eun Sang Choi, C. dela Cruz, M. O. Ajeesh, Eliana S. Krakovsky, Daniel A. Rehn, Jie Xing, Athena S. Sefat, Minhyea Lee. 2025-10-24. Field-induced magnetic phase transition driven by a ground state level-crossing in CsErSe$_2$. https://arxiv.org/abs/2510.21616

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