Coherent THz-wave emission from voltage-and number-controlled intrinsic Josephson junctions in Bi-2212

Intense and coherent terahertz electromagnetic wave (THz-wave) emission from the intrinsic Josephson junctions (IJJs) in single crystalline high-Tc superconductor Bi2Sr2CaCu2O8+δ (Bi-2212) was reported in 2007 [L. Ozyuzer \textit{et al}., Science \textbf{318}, (2007) 1291.]. In the present work, we demonstrate the relationship between the bias condition and the resonance state by controlling both the applied voltage, V, and the number of resistive junctions, N. We directly observed that if N junctions are in resistive state, the resonance frequency, fJ, varies in accordance with the ac-Josephson relation; fJ = (2|e|/h)V/N, although frequency fJ has previously been thought to be uniquely determined by the geometrical condition due to the cavity resonance effect [M. Tsujimoto \textit{et al}., Phys. Rev. Lett. \textbf{105}, (2010) 037005.]. We also found that the emission intensity varies as a function of both fJ and N. *CREST-JST, WPI-MANA, Strategic Initiative A (University of Tsukuba