INVITED PAPER Special Progress Physics Applications Josephson Approaches to High Performance Terahertz-Waves Emitting Devices Utilizing Single Crystals of High Temperature Superconductor Bi₂Sr₂CaCu₂O₈₊

Our group has developed terahertz(THz)-waves emit-ting devices utilizing single crystals of high temperature superconductor Bi2Sr2CaCu2O8+& delta; (Bi2212). The working principle of the device is based on the AC Josephson effect which is originated in the intrinsic Josephson junctions (IJJs) constructed in Bi2212 single crystals. In principle, based on the superconducting gap of the compound and the AC Josephson ef-fect, the emission frequency range from 0.1 to 15 THz can be generated by simply adjusting bias voltages to the IJJs. In order to improve the device performances, we have performed continuous improvement to the device structures. In this paper, we present our recent approaches to high perfor-mance Bi2212 THz-waves emitters. Firstly, approaches to the reduction of self Joule heating of the devices is described. In virtue of improved de-vice structures using Bi2212 crystal chips, the device characteristics, such as the radiation frequency and the output power, become better than pre-vious structures. Secondly, developments of THz-waves emitting devices using IJJs-mesas coupled with external structures are explained. The re-sults clearly indicate that the external structures are very useful not only to obtain desired radiation frequencies higher than 1 THz but also to con-trol radiation frequency characteristics. Finally, approaches to further un-derstanding of the spontaneous synchronization of IJJs is presented. The device characteristics obtained through the approaches would play impor-tant roles in future developments of THz-waves emitting devices by use of Bi2212 single crystals.