Effects of orientational and positional randomness of particles on photonic band gap

A recent work [Phys. Rev. Lett. 126, 208002 (2021)] has explored how thermal noise-induced randomness in a self-assembled photonic crystal affects photonic band gaps (PBGs). For the system of a two-dimensional photonic crystal composed of a self-assembled array of rods with square cross sections, it was found that its PBGs can exist over an extensive range of packing densities. Counterintuitively, at intermediate packing densities, the transverse magnetic (TM) band gap of the self-assembled system can be larger than that of its corresponding perfect system (rods arranged in a perfect square lattice and having identical orientations). Due to shape anisotropicity, the randomness in the self-assembled system contains two kinds of randomness, i.e., positional and orientational randomness of the particles. In this paper, we further investigate how PBGs are influenced solely by positional or orientational randomness. We find that compared to the perfect situation, the introduction of only orientational randomness decreases the transverse electric (TE) band gap whereas having no obvious effects on the TM band gap. In contrast, the introduction of only positional randomness decreases the TE band gap significantly, whereas it can widen or narrow the TM band gap, depending on the packing density. We also discuss the thermal (i.e., self-assembled) system where two kinds of randomness are present. Our paper contributes to a better understanding of the role orientational randomness and positional randomness play on PBGs and may benefit the PBG engineering of photonic crystals through self-assembly approaches.

Automated summary

A recent study investigated the impact of thermal noise-induced randomness on photonic band gaps (PBGs) in self-assembled photonic crystals. The study revealed that PBGs can exist in a two-dimensional photonic crystal composed of a self-assembled array of rods with square cross sections. Moreover, the introduction of positional or orientational randomness affects the PBGs, providing insights for PBG engineering and understanding the role of randomness in photonic crystals.