Topological magnonic dislocations modes

TL;DR

This paper demonstrates the existence of topologically protected magnonic modes localized at dislocations in 2D ferromagnets, revealing their robustness and the relationship between lattice defects and spin excitation spectra.

Contribution

It introduces magnonic dislocation modes characterized by a $Z_2$ topological invariant, showing their robustness against disorder and lattice imperfections.

Findings

Existence of topologically protected magnonic modes at dislocations

These modes are characterized by a $Z_2$ invariant

Bulk topology remains robust under lattice defects

Abstract

Spin fluctuations in two-dimensional (2D) ferromagnets in the presence of crystalline lattice dislocations are investigated. We show the existence of topologically protected non-propagative modes that localize at dislocations. These in-gap states, coined as {\it magnonic dislocation modes}, are characterized by the $Z_2$ topological invariant that derives from parity symmetry broken induced by sublattice magnetic anisotropy. We uncover that bulk topology existing in the perfect crystal is robust under the influence of lattice defects, which is monitored by the real-space Bott index. It is also revealed that the topology of {magnonic dislocation modes} remains unaffected when bulk topology becomes trivial and is remarkably resilient against magnetic disorder. Our findings point to the intriguing relationship between topological lattice defects and the spectrum of topological spin excitations.