# Propagating spin excitations along skyrmion strings

## TL;DR

This study demonstrates the experimental and theoretical analysis of coherent, non-reciprocal spin excitation propagation along skyrmion strings in a chiral magnet, revealing long-range transfer potential for topological information processing.

## Contribution

It provides the first experimental evidence and theoretical understanding of directional spin excitation propagation along three-dimensional skyrmion strings.

## Key findings

- Spin excitations propagate over distances exceeding 10^3 times the skyrmion diameter.
- Propagation is directionally non-reciprocal and mode-dependent.
- Theoretical dispersion matches experimental observations.

## Abstract

Magnetic skyrmions, topological solitons characterized by a two-dimensional swirling spin texture, have recently attracted attention as stable particle-like objects. In a three-dimensional system, a skyrmion can extend in the third dimension forming a robust and flexible string structure, whose unique topology and symmetry are anticipated to host nontrivial functional responses. Here, we experimentally demonstrate the coherent propagation of spin excitations along skyrmion strings for the chiral-lattice magnet Cu2OSeO3. We find that this propagation is directionally non-reciprocal, and the degree of non-reciprocity, as well as the associated group velocity and decay length, are strongly dependent on the character of the excitation modes. Our theoretical calculation establishes the corresponding dispersion relationship, which well reproduces the experimentally observed features. Notably, these spin excitations can propagate over a distance exceeding 10^3 times the skyrmion diameter, demonstrating the excellent long-range nature of the excitation propagation on the skyrmion strings. Our combined experimental and theoretical results offer a comprehensive account of the propagation dynamics of skyrmion-string excitations, and suggest the possibility of unidirectional information transfer along such topologically-protected strings.