Controlled Defects on the Vortex Phases and Dynamics of High-Temperature and Conventional Amorphous Superconductors -- From DC to Microwave Frequencies

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9401315 Yeh technical abstract: The effects of controlled defects on the vortex phases and dynamics of high-temperature and conventional superconductors will be investigated by systematically varying the type and density of defects in the superconducting samples. In particular, the role of zero, one, and two-dimensional defects, as well as their interplay on the vortex phases and the phase transitions, will be studied by measurements of low-frequency (dc- 10 MHz) electrical transport and magnetic properties. The samples are yttrium barium copper oxide single crystals with controlled densities of point and columnar defects. In addition, the microwave vortex dynamics associated with the local pinning properties of superconductors wil be compared with the critical dynamics obtained at lower frequencies. Non-technical abstract: The presence of defects in superconductors plays an important role in determining their response to external electromagnetic fields and their tolerance to the increase of temperature. The main theme of this work is to investigate the effects of controlled defects on the properties of high temperature and conventional superconductors in large applied magnetic fields. Information learned from this investigation can lead to optimizarion of the properties of these superconductors for a variety of applications in large magnetic fields, including microwave components for communication signal detection and processing, as well as high performance superconducting magnets. ***