Rotating Spin Wave Modes in Nanoscale M\"obius Strips

TL;DR

This study explores how the unique topology of M"obius nanostrips influences spin-wave modes, revealing non-reciprocal dispersion and topologically induced effects that can be harnessed for advanced magnonic device engineering.

Contribution

It demonstrates the impact of M"obius topology on spin-wave behavior, including mode splitting and non-reciprocal dispersion, through micromagnetic simulations and analytical modeling.

Findings

M"obius geometries exhibit non-degenerate mode doublets due to twist-induced geometric phase.

The topology causes non-reciprocal dispersion relations and half-integer wavelength quantization.

Analytical models accurately reproduce the observed dispersion behavior.

Abstract

Curved and topologically nontrivial magnetic structures offer new pathways to control spin-wave behavior beyond planar geometries. Here, we study spin-wave dynamics in M\"obius-shaped soft-magnetic nanostrips using micromagnetic simulations. By comparing single-, double-, and triple-twisted M\"obius strips to a topologically trivial bent ring, we isolate the roles of helical twist and non-orientable topology. M\"obius geometries exhibit non-degenerate mode doublets associated with counterpropagating spin waves, in contrast to the standing-wave doublets in the trivial case. This splitting arises from a twist-induced geometric (Berry) phase that breaks propagation symmetry, producing non-reciprocal dispersion relations. The M\"obius topology further imposes antisymmetric boundary conditions, resulting in half-integer wavelength quantization. Local RF excitation allows for the selective generation of spin waves with defined frequency and direction. An analytical model reproduces the dispersion behavior with excellent agreement. These results highlight how geometric and topological design can be leveraged to engineer spin-wave transport in three-dimensional magnonic systems.