Multiply coated microspheres. A platform for realizing fields-induced structural transition and photonic bandgap

Under crossed electric and magnetic fields, multiply coated microspheres fo rm columnar crystallites with an internal structure that transforms from bo dy-centered-tetragonal to face-centered-cubic as the ratio between the magn etic and the electric fields exceeds a minimum value. The observed transiti on scenario is in excellent agreement with calculations. These multiply coa ted microspheres also serve as building blocks for photonic crystals. Robus t photonic gaps exist in any periodic structure built from such spheres whe n the filling ratio of the spheres exceeds a threshold.