Tunable Photonic Band Gaps in an Entropic Crystal

Materials adopting the diamond structure exhibit many useful properties across atomic and colloidal systems, and therefore have been a strong research focus in materials science. The desirable properties of the diamond structure pose an interesting opportunity for reconfigurable materials: can we create a material that naturally transitions reversibly to and from the diamond structure? Hypothetically, such a material could exhibit two states, an on state, in which it exhibits the striking properties tied to the diamond structure, and an off state, where one or more of these properties are no longer present. In this talk, we show that we can design a colloidal crystal from convex polyhedral particles with a complete photonic band gap in the on state, which disappears when the material is switched off by a shape- and pressure-induced phase transition.