Theoretical studies for the intrinsic Josephson effect and the collective excitations in high-Tc superconductors

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The CuO2 layers in high-Tc cuprates are responsible for the high-temperature superconductivity in these systems. The coupling between Cu02 layers in high-Tc superconductors is very weak. As a result, the Josephson effect appears in the c-axis transport phenomena even in single crystals of these superconductors, which is called the intrinsic Josephson effect. In this research project I have investigated theoretically the c-axis transport properties related to the intrinsic Josephson effects in high-Tc superconductors. I have constructed a complete quantum theory for the Josephson plasma oscillations observed in these superconductors. The effects of the quasi-particles on the plasma excitations were clarified in this theory. The c-axis charge dynamics in an array of the intrinsic Josephson junctions reveals the size dependence when the in-plane (ab-plane) area is decreased. This phenomena is caused by the Coulomb blockade effect. The plasma oscillations in this system become unstable when the in-plane area decreases below some critical value, Wc. The c-axis charge dynamics in the system with an in-plane area less than Wc is dominated by the single Cooper-pair tunneling. I have developed a renormalization group theory for the Coulomb blockade effect in an array of the intrinsic Josephson junctions. The explicit expression for Wc was derived.