| Summary: | 碩士 === 輔仁大學 === 物理學系 === 88 === This thesis work is divided into two parts. The first part is investigation of magnetorseistance in spin-valves systems. In the second part, we studied the charge transport mechanism in all superconductor single-electron transistors.
In the first part of this work. We inserted thin magnetic layer at the interface in spin-valves, and found that magnitude of the giant magneto-resistance is determined largely by the character of magnetic/nonmagnetic interfaces. The samples were prepared by DC magnetron sputtering in a high vacuum system. The MR properties were measured at room temperature using four-terminal method. The magnetic hysteresis curves were obtained by MOKE. The results indicated that the interfacial scattering due to magnetic impurity is important. We also noticed that the thickness of nonmagnetic layer play a critical role in producing the GMR effect. When the thickness of nonmagnetic layer is thin, strong ferromagnetic coupling between magnetic layers would suppress the spin-valves effect. In the opposite case, when the nonmagnetic layer is too thick spin-dependent mean free path is not enough to diffuse into magnetic layer to induce scattering and the GMR effect is small.
In the second part of this work, we fabricated super-conducting single electron transistors, and measured them at temperature down to mK. The small capacitance of the center island gives rise to Coulomb energy barrier, which is the origin of the Coulomb Blockade phenomenon seen in these transistor. The transport measurments showed structures in the current- voltage characteristics due to cooper pair and quasiparticle tunneling. These structures including quasiparticle tunneling 、Josephson-Quaisparticle process and other high order tunneling process, oscillate with the gate voltage with a period corresponding to change of one electron on the island. From the tunneling rate calculations, we can calculate the current-voltage characteristics which agree well with our measured data.
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