Broadly Tunable Sub-terahertz Emission from Internal Branches of the   Current-voltage Characteristics of Superconducting Bi2Sr2CaCu2O8+d Single   Crystals
  Continuous, coherent sub-terahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O8+d single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the ac Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed. 
Manabu Tsujimoto, Takashi Yamamoto, Kaveh Delfanazari, Ryo Nakayama,   Takeo Kitamura, Masashi Sawamura, Takanari Kashiwagi,...
cond-mat.supr-con