Intrinsic Josephson Junctions and their Terahertz Functions

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High-Tc superconducting cup per oxides (HTSC) show strong anisotropies due to their layered crystal structures consisting of the superconducting CuO_2 layers and the insulating or normal conducting layers in between them. In particular, current transport behaviors across the layers are governed by Josephson weak coupling and are termed the intrinsic Josephson effects. Junction devices fabricated of the HTSC single crystals to use the intrinsic Josephson effects are the intrinsic Josephson junctions (IJJ). The IJJ is the only HTSC Josephson device which can exploit the large energy gaps characteristic of the HTSC and expected to be useful devices operating at very high frequencies up to the terahertz regime. This research project aims to reveals high frequency properties of IJJ to develop superconducting solid state devices for detection and oscillation of terahertz waves. We study (1)precise control of junction properties and (2)effects of externally applied electromagnetic waves on th … More e collective motion of Josephson vortices in the IJJ.For (1), we develop a novel method to control the junction properties by the ion implantation of impurities with strong oxygen affinities.For(2), we succeeded to observe high frequency responses on the vortex flow state which is generated by a flux-flow experiment system designed for this research consisting of a compact cryo-cooler and permanent magnets. By using this system, we found a remarkable zero-crossing step that indicates phase-locking of moving Josephson vortices to the externally applied electromagnetic waves. This results is quite important because it is evident that the electromagnetic waves drives Josephson vortices or vice versa and applicable to amplification and oscillation of terahertz waves by using IJJ. Furthermore, we found periodic potentials introduced in the IJJ along the direction of vortex motion is effective to develop the in-phase coherent motion of the Josephson vortices over the IJJ that is a key point to realize the efficient emission of electromagnetic waves from the IJJ. Less