Additionally, nanostructuring—altering the material's structure at the nanoscale—has emerged as a powerful method to engineer band gaps. Despite its potential, Band Gap Engineering faces challenges, ...

(a) Schematics of phononic crystal of different dimensionalities. (b) An example of phonon band structure. The orange area marks the forbidden band gap. (c) Examples of phononic crystals efficient at ...

An insulator has a band structure in which occupied and empty bands are separated by an energy gap. The existence of an energy gap, however, does not guarantee that a material is a simple insulator.