Inducing symmetry breaking in nanostructures: anisotropic stretch-tuning photonic crystals.

We use elastically induced phase transitions to break the structural symmetry of self-assembled nanostructures, producing significantly modified functional properties. Stretching ordered polymer opals in different directions transforms the fcc photonic crystal into correspondingly distorted monoclinic lattices. This breaks the conventional selection rules for scattering from the crystal planes, yielding extra multiply scattered colors when the phase-breaking stretch is in specific directions. Scattering is spectroscopically tracked in real time as the samples distort, revealing a new phase transition that appears for <121>-oriented deformations.