Engineering short-range correlation in bi-disperse self-assembled photonic structures

Short-range correlations in disordered photonic structures composed of sub-micrometer scatterers can give rise to correlation-driven photonic gaps. However, methods to systematically tune such structural correlations remain limited. Here, we investigate that the scatterer size ratio (β) in self-assembled bi-disperse photonic structures provides a pathway to engineer short-range correlations and hence the photonic gaps. Correlation-induced reflectivity peaks, accompanied by simultaneous dips in both the transport (lt) and scattering (ls) mean free paths, emerge over the range of 0.77 < β < 0.83. Further reduction in β value suppresses short-range correlations and consequently eliminates the photonic gap. Pair correlation and structure factor analyses reveal that the observed transition from well-resolved to vanishing gaps is driven by the breakdown of short-range correlations. Experimentally extracted lt and ls further show that enhanced backscattering is associated with short-range correlations. Moreover, tuning the β value not only shifts the gap wavelength but also modulates its strength, as supported by finite-difference time-domain simulations. Together, these results advance disorder-enabled design strategies for photonic materials, enabling precise control of scattering and bandgap characteristics.