Measurements of thermodynamical physical properties of High Tc Superconducting Thin Film

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Following three subjects have been investigated.A. AC Impedance of Thin-Film Bi-Sr-Ca-Cu-OIn many electronic devices based on high-temperature (high-TC) superconductors (HTS), the thin-film HTS are invariably subjected to an alternating (AC) or pulsed current. In contrast, our work concentrated on the magnitude and phase of impedance z for large values of J. Experiments were conducted on an epitaxial film of Bi-Sr-Ca-Cu-O. The results indicated that for 500kHz and above, z increased with increasing frequency. These results could be qualitatively explained by assuming that magnetic flux vortices were present in the film.B. Heat Transfer and Thermoelectric Voltage at Metallic Point ContactsSince it had already been demonstrated that a Point-contact (PC) between even similar metals can generate a thermoelectric voltage, the use of PC's as microscale temperature sensors seemed promising. At temperatures ranging from 85 K to room temperature, a thermoelectric voltage was shown to exist even … More at the Ag-Ag PC, in accordance with the previous results. This thermoelectric voltage was conveniently plotted against the nondimensionalized substrate temperature, demonstrating the feasibility of employing a PC as a temperature sensor. It was shown that the heat flux along the metal whisker is a linear function of the temperature drop across the PC for small temperature drops, but becomes nonlinear for large temperature drops.C. Film/Substrate Thermal Boundary Resistance for an Er-Ba-Cu-O High-TC Superconducting FilmThe thermal design and operation of thin-film high-TC electronics at low temperatures depends crucially on the thermal contact resistance at the boundary between the film and the substrate (Rbd). In our experimental investigation, Rbd for an Er-Ba-Cu-O film deposited on an MgO substrate, was measured by a technique in which the superconducting film was etched into two adjacent strips. One strip supported a large bias current and served as the heater, while the other strip carried a much smaller current, and served to measure the temperature of the substrate. The principal conclusion drawn from our results was that Rbd was at least two orders of magnitude higher than the previously reported values. Less