Flatband Line States in Photonic Super-Honeycomb Lattices

TL;DR

This paper experimentally demonstrates novel flatband line states in a photonic super-honeycomb lattice, revealing topologically protected band crossings and unique localized states not achievable by conventional methods.

Contribution

It introduces a new topological flatband state in a photonic super-honeycomb lattice, expanding understanding of flatband systems and topological phenomena in photonics.

Findings

Demonstrated two distinct flatband line states in sHCL

Observed topologically protected band crossings in the spectrum

Identified unique zigzag-line states not seen in other lattices

Abstract

We establish experimentally a photonic super-honeycomb lattice (sHCL) by use of a cw-laser writing technique, and thereby demonstrate two distinct flatband line states that manifest as noncontractible-loop-states in an infinite flatband lattice. These localized states (straight and zigzag lines) observed in the sHCL with tailored boundaries cannot be obtained by superposition of conventional compact localized states because they represent a new topological entity in flatband systems. In fact, the zigzag-line states, unique to the sHCL, are in contradistinction with those previously observed in the Kagome and Lieb lattices. Their momentum-space spectrum emerges in the high-order Brillouin zone where the flat band touches the dispersive bands, revealing the characteristic of topologically protected bandcrossing. Our experimental results are corroborated by numerical simulations based on the coupled mode theory. This work may provide insight to Dirac like 2D materials beyond graphene.