Emission of terahertz electromagnetic wave in intrinsic Josephson junction stacks

We overview our recent theoretical works on the emission of terahertz electromagnetic waves recently observed by Ozyuzer et al in the current-biased Bi-2212 intrinsic Josephson junctions. In the voltage state the Josephson current oscillates with a frequency ω = (2e/)(V/N), N being the number of voltage junctions in a stack of intrinsic Josephson junctions. When the frequency ω coincides with an eigen mode frequency of the stacks, strong emission of the electromagnetic wave takes place. We performed numerical simulations for two 2D models composed of intrinsic Josephson junctions and the outside vacuum and clarified the pattern of emitted electromagnetic waves.