Flux-mediated effective Su–Schrieffer–Heeger model in an impurity decorated diamond chain

In photonic flat-band (FB) systems, which are characterized by a halting of light transmission, perturbations can play a major role in determining the transport properties of the system. In this work, this is exploited by purposefully including impurities in a photonic diamond chain with a constant synthetic flux per plaquette so that an effective system of choice can be tailored from the FB. By tuning both the separation between impurities and the flux value, any coupling distribution can be engineered. The effective system can also exhibit a nontrivial topology as we demonstrate by imprinting a Su–Schrieffer–Heeger model on the diamond chain, which is further shown to have enhanced robustness to disorder due to the extension of the impurity modes. Furthermore, effective non-Hermitian systems can also be realized by employing complex-valued impurities. We propose an implementation of the system in a lattice of optical waveguides carrying orbital angular momentum modes, where a phase in the coupling can be included and controlled geometrically. There, variations of the refractive index of chosen waveguides generate detunings that act as impurities, which couple together to form the effective system. This work opens the way for the design of topologically nontrivial models in other FB systems, or in other physical platforms.