Device-Oriented Basic Studies on Coherent Quantum Waves in Josephson Superlattices

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The purpose of this study is to establish the fundamentals of quantum effect devices using dynamic behavior of coherent waves of electrons (holes) and flux quanta in natural superlattices of intrinsic Josephson junctions, which consist of superconducting CuOィイD22ィエD2 and insulating BiO/SrO layers, in layered high-temperature oxide-superconductor BiィイD22ィエD2SrィイD22ィエD2CaCuィイD22ィエD2OィイD2yィエD2 single crystals.The results obtained in this study are as follows :1. For rectangular and annular mesas (superlattices) fabricated as basic shapes of the devices from the single crystals, it has been clarified that the coherent motion of flux quanta (Josephson vortices) introduced by applying magnetic fields to the mesas occurs at high rates of (1-5)×10ィイD1-6ィエD1m/s (at 4.2K) by biasing currents to the mesas, which correspond nearly to the highest phase velocity of electromagnetic waves induced in the constituent intrinsic Josephson junctions. Numerical simulations have also shown such a motion of flux quanta in the superlattices.2. For rectangular mesas, it has been found that high frequency oscillations, which take place due to the motion of flux quanta in the intrinsic Josephson junctions, can be controlled by external magnetic fields, and as a result, a high frequency oscillation of 80GHz occurs with a magnetic field of 0.16T at 4.2K.3. For rectangular and annular mesas, it has also been found that the coherent motion of electronic (hole) waves in the intrinsic Josephson junction superlattices can be excited and controlled as in switching devices by current pulses, and then high frequency oscillations of several ten GHz-THz (at 4.2K) can also occur.