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arXiv · 2605.24527

Emergent Dispersive Multipolar Excitations in NaErSe$_{2}$

Zheng Zhang·Mingfang Shu·Mingtai Xie·Weizhen Zhuo·Yanzhen Cai·Christian Balz·Jianting Ji·Feng Jin·Jie Ma
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Abstract

In most condensed-matter systems, local and collective excitations remain decoupled due to their distinct energy scales. Here, we identify coupled local-collective excitations in the triangular antiferromagnet NaErSe$_2$ by combining neutron spectroscopy with total angular momentum modeling. The low-lying crystalline electric field (CEF) doublets include a dipolar $\Gamma_4$ ground state forming stripe-$x$ order and a $\Gamma_{5,6}$ excited state with dipole-octupole character. High-resolution spectra reveal emergent symmetry-selected dispersions, where magnon branches from the ground state are replicated on higher $\Gamma_4$ levels but couple with the $\Gamma_{5,6}$ levels to form a distinct multipolar band. An applied magnetic field reconstructs the CEF wavefunctions and polarizes the system into a multipolar ferromagnet, further reshaping the spectra. This study demonstrates the emergent coupling of local and collective excitations driven by strong spin-orbit coupling and establishes NaErSe$_2$ as a platform for field-tunable multipolar excitations in frustrated magnets.

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Zheng Zhang, Mingfang Shu, Mingtai Xie, Weizhen Zhuo, Yanzhen Cai, Christian Balz, Jianting Ji, Feng Jin, Jie Ma. 2026-05-23. Emergent Dispersive Multipolar Excitations in NaErSe$_{2}$. https://doi.org/10.1103/7k9l-j1kh

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