Surface states in photonic crystals

The propagation of surface electromagnetic waves along photonic crystal (PC) boundaries is examined. It is shown that in a number of cases, these are backward waves. The nature of surface electromagnetic states localized at the PC boundary is discussed; these states transfer no energy along the boundary (their tangential wave number is zero). An analogy with the well-known Tamm and Shockley surface states in solid state physics is drawn. It is shown that in the case of a PC, both types of states can be regarded as Tamm states. Experimental results on the observation of surface states are presented. A system using an external magnetic field to control a surface state is considered.