Experimental observation of edge states in SSH-Stub photonic lattices

Gabriel Cáceres-Aravena,Diego Guzmán-Silva,Rodrigo A Vicencio,Bastián Real,Alberto Amo,Luis E F Foa Torres

doi:10.1103/physrevresearch.4.013185

Abstract

We reveal unconventional edge states in a one-dimensional Stub lattice of coupled waveguides with staggered hoppings. The edge states appear for the same values of hoppings as topological edge states in the Su-Schrieffer-Heeger model. They have different energies depending on the lattice termination and present a remarkable robustness against certain types of disorder. We evidence experimentally the phase transition at which these edge states appear, opening the door to the engineering of one-dimensional lattices with localized edge modes whose energy and location can be controlled at will.

Highlights

During the last few years, there has been a surge of interest in the study of topological edge states in a plethora of systems, ranging from electronic states in materials [1] to analogs in mechanical [2] and photonic settings [3,4]
The edge states enjoy a robustness comparable to those found in the SSH model; our results open a path for robust edge states beyond the standard topological classification
We find that γ = −δ and βzh = 0 for |δ| < 1, which is the same existence condition of the two previous edge states

Summary

INTRODUCTION

During the last few years, there has been a surge of interest in the study of topological edge states in a plethora of systems, ranging from electronic states in materials [1] to analogs in mechanical [2] and photonic settings [3,4]. Beyond the much sought-for topological protection, a few studies [5–8] have shown that sometimes an enhanced robustness (and even antifragile behavior) can be achieved by breaking the rules and tinkering with edge states outside the topological phase. This includes, for example, edge states coexisting with a gapless bulk [5], states of metals on topological insulator systems [6], and many Floquet systems [7,8] which are effectively gapless but which show robust edge states. One may wonder whether when going beyond the constraints of topology one could find edge states robust to those of the paradigmatic SSH model. The edge states enjoy a robustness comparable to those found in the SSH model; our results open a path for robust edge states beyond the standard topological classification

SSH-STUB MODEL

EXPERIMENTAL DEMONSTRATION

DISCUSSION