Emergent Dispersive Multipolar Excitations in NaErSe_{2}.

In most condensed-matter systems, local and collective excitations remain decoupled due to their distinct energy scales. Here, we identify the coupled local-collective excitations in the triangular antiferromagnet NaErSe_{2}, by combining neutron spectroscopy with a total angular momentum modeling. The low-lying crystalline electric field (CEF) doublets include a dipolar Γ_{4} ground state forming a stripe-x order and a Γ_{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 Γ_{4} levels but couple with the Γ_{5,6} levels to form a distinct multipolar band. An applied magnetic field reconstructs the CEF wave functions and polarizes the system into a multipolar ferromagnet, further reshaping the spectra. The 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.