# Valley Hall phases in Kagome lattices

## TL;DR

This paper demonstrates the existence of valley Hall effects in Kagome lattice phononic systems caused by mirror and inversion symmetry breaking, leading to topologically protected edge states and unidirectional wave propagation.

## Contribution

It reveals that mirror symmetry breaking can induce valley Hall phases in phononic Kagome lattices, expanding understanding of topological effects in mechanical systems.

## Key findings

- Valley Chern numbers arise from symmetry breaking.
- Protected edge states exist at lattice interfaces.
- Unidirectional wave propagation observed in finite systems.

## Abstract

We report the finding of the analogous valley Hall effect in phononic systems arising from mirror symmetry breaking, in addition to spatial inversion symmetry breaking. We study topological phases of plates and spring-mass models in Kagome and modified Kagome arrangements. By breaking the inversion symmetry it is well known that a defined valley Chern number arises. We also show that effectively, breaking the mirror symmetry leads to the same topological invariant. Based on the bulk-edge correspondence principle, protected edge states appear at interfaces between two lattices of different valley Chern numbers. By means a plane wave expansion method and the multiple scattering theory for periodic and finite systems respectively, we computed the Berry curvature, the band inversion, mode shapes and edge modes in plate systems. We also find that appropriate multi-point excitations in finite system gives rise to propagating waves along a one-way path only.