If you've read this blog for any period of time, you will have seen that, as many times as I can, I try to highlight the application side of physics. This is because a lot of people who are not familiar with the field tend to think that physics is only the LHCs, the Brian Greenes, the particle physics, the String theories, etc. If I can't contribute anything to physics, I want to at least contribute to destroying such myth.
This is one such example. APS Physics has recently highlighted a landmark paper that marked the birth of the idea of photonic crystals.
Semiconductors and band insulators are material that has a gap in the electronic band structure. On the other hand, photonic crystals have gaps in the photonic band band structure, whereby the material simply does not propagate photons having energies within that gap.
You may read the article to find out what applications such materials are good for.