THz generation using Fluxon dynamics in high temperature superconductor Josephson junctions

Ever since the Josephson junction was discovered, the possibility of generating high frequency radiation has been considered. Such radiation could have many applications, for example as a local oscillator in an integrated receiver, a spectrometer, an imaging device etc. A brief historical overview of methods and results will be presented. Special emphasis will be given to the BSCCO--type high temperature superconductors that may be considered as a stack of coupled Josephson junctions - potentially having applications as terahertz oscillators. The stack of inductively coupled long Josephson junctions is modeled as a system of coupled sine-Gordon equations. The key point for oscillator applications is to have in-phase coherent motion of fluxons in the different Josephson junctions in the stack. This may be obtained by applying a (large) magnetic field parallel to the layers, or by having the system interacting with a cavity. In both cases the fluxon dynamics is very non-linear, and numerical simulations are necessary. We will also present a few cases where analytical results have provided a new insight in this complicated non-linear system.