Can we design a reconfigurable photonic crystal in the visible light range?*

Crystals with a complete photonic band gap are materials composed of mixed dielectric media which result in the reflection of all electromagnetic waves in a given range of wavelengths, commensurate to the length scale of the crystal, and pose an exciting avenue for novel materials. Diamond is a popular target for photonic crystals, which poses an opportunity for reconfigurable matter: can we create a colloidal crystal that switches reversibly to and from the diamond structure? Drawing inspiration from high-pressure phase transitions of diamond-forming atomic systems, we design a system of particles with polyhedral shapes that transitions from diamond to a tetragonal diamond derivative upon a small change in pressure and coincides with a noteworthy modulation of the photonic properties of the crystal. We propose that the transition provides a reversible reconfiguration process for a potential new colloidal material, and we draw parallels between this transition and the materials from which we take inspiration.