Diameter-Controlled High-Order Vortex States and Magnon Hybridization in VSe2 Nanotubes

Abstract: Curved magnets offer a rich phase diagram and hold great promise for next-generation spintronic technologies. This study establishes the paramount significance of high-order vortex states (e.g., 3$\varphi$ with winding number $n$ > 1) in VSe2 nanotubes, which uniquely enable magnonic functionalities fundamentally inaccessible to conventional magnetic systems. These states arise from diameter-dependent competition between the nearest-neighbor ferromagnetic ($J_1$) and longer-range antiferromagnetic ($J_2$/$J_3$) couplings, as rigorously validated through density-functional theory calculations and Heisenberg modeling of phase diagrams. Critically, by the Landau-Lifshitz-Gilbert equation, we find that high-order vortex configurations unlock an intrinsic hybridization mechanism governed by strict orbital angular momentum (OAM) selection rules ($\Delta l = \pm 2(n-1)$) -- a process strictly forbidden in fundamental vortices ($n$ = 1) -- generating complex high-OAM magnons with measurable topological charge. This is vividly demonstrated in the 3$\varphi$ state, where hybridization between $l$ = -4, 0 and 4 modes produces eight-petal magnon density patterns. Such states provide an essential platform-free solution for generating high-OAM magnons, wchich is crucial for spin-wave-based information transport. These findings establish a predictive theoretical framework for controlling high-order vortex states in curved magnets and highlight VSe2 nanotubes as a promising platform for exploring complex magnetism and developing future magnonic and spintronic devices.