# Symmetry and localization properties of defect modes in magnonic superlattices

## TL;DR

This paper investigates how the symmetry and localization of defect modes in a one-dimensional magnonic superlattice can be controlled through geometry, enabling flat and symmetric or antisymmetric spin-wave modes for potential microwave device applications.

## Contribution

It introduces a theoretical framework for controlling defect mode symmetry and flatness in magnonic superlattices via geometric design, supported by numerical simulations.

## Key findings

- Transition from dispersive to flat defect modes with geometry control
- Symmetric or antisymmetric defect modes can be selectively excited
- External magnetic field has limited effect on antisymmetric mode position

## Abstract

Symmetry and localization properties of defect modes of a one-dimensional bi-component magnonic superlattice are theoretically studied. The magnonic superlattice can be seen as a periodic array of nanostripes, where stripes with different width, termed as defect stripes, are periodically introduced. By controlling the geometry of the defect stripes, a transition from dispersive to practically flat spin-wave defect modes can be observed inside the magnonic band gaps. It is shown that the spin-wave profile of the defect modes can be either symmetric or antisymmetric, depending on the geometry of the defect. Due to the localized character of the defect modes, a particular magnonic superlattice is proposed, wherein the excitation of either symmetric or antisymmetric flat magnonic modes is enabled at the same time. Also, it is demonstrated that the relative frequency position of the antisymmetric mode inside the band gap does not significantly change with the application of an external field, while the symmetric modes move to the edges of the frequency band gaps. The results are complemented by numerical simulations, where an excellent agreement is observed between both methods. The proposed theory allows exploring different ways to control the dynamic properties of the defect modes in metamaterial magnonic superlattices, which can be useful for applications on multifunctional microwave devices operating over a broad frequency range.