Demonstration of Robust Boundary Modes in Photonic Decorated Honeycomb Lattices

摘要

The decorated honeycomb lattices (DHLs) represent a typical model thatevinces nontrivial chiral spin liquid and rich topological insulating phases incondensed matter physics, yet in natural materials such lattice structures arenot commonly found. Here, a photonic DHL that exhibits two singular flatbands is experimentally demonstrated, thereby observing two distinct robustboundary modes (RBMs) associated with each flat band. These RBMs rely onspecially tailored open boundaries in the flatband lattice with wavefunctionsingularities due to band-touching, manifesting topological noncontractibleloop states that cannot be simply constructed from superposition of conventionalflatband states. The robustness of such boundary modes to perturbationsis also examined, corroborated by numerical simulations and theoreticalanalysis. This work illustrates a photonic platform exhibiting Dirac cones,singular band-touching and multiple flat bands that may be employed tostudy exotic flatband phenomena and topological insulating phases in opticsand beyond.