Physics
Scientific paper
Jan 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992phdt........82h&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF SOUTH FLORIDA, 1992.Source: Dissertation Abstracts International, Volume: 53-03, Section: B, page:
Physics
Superconductors, Yttrium Barium Copper Oxide, Barium Copper Oxide
Scientific paper
The characteristics of thin-film rm YBa_2Cu_3O_7 superconductors were studied from the superconducting region through the transition region and into the normal region. The properties studied included the resistance-temperature, current-voltage, and electrical noise with concentration of measurements in the transition region. The resistance vs. temperature measurements show a zero resistance followed by a small rise in magnitude at the onset of resistance followed by a sharp increase until the resistance tapers off in the fully normal region. The a-axis films had a larger normal resistivity, a lower critical temperature (T_ {c0}), and a broader transition than the similar c-axis films. The current (I)-voltage (V) measurements were concentrated in the transition region. A power relation between I and V was found to be V~ I ^{a(T)} where a(T) is temperature dependent starting high the onset of vortex formation, approaches 3 at the vortex unbinding temperature, and goes to 1 when fully normal. This behavior was predicted by the Kosterlitz-Thouless theory and was experimentally in all four films measured. The current-induced electrical noise characteristics were measured for four samples varying in thickness and axis orientation. Each film exhibited a widely varying magnitude of the noise voltage spectral density (S V) in the transition region with a leveling off when fully normal. The normalized noise (SV/V^2) showed a sharp decrease in magnitude from the onset of measurable noise continually decreasing until flattening out when fully normal. The a-axis films exhibited S V/V^2 over 3 order of magnitude larger than the c-axis films in the transition and normal regions. The normalized temperature coefficient of resistance (beta) was plotted against SV/V^2 on a log-log scale to see if the noise generated was due to temperature fluctuations (slope = 2). The four films all had slopes of greater than 4 revealing that the temperature fluctuations were not the cause of the noise in the transition region. The generating mechanisms behind 1/f^2 voltage spectra were investigated. The traditional voltage ramp, usually considered the cause of the 1/f ^2 signal, was shown both theoretically and experimentally to show no measurable output signal when using an amplification system. The 1/f^2 signal was generated using a changing resistance and exhibited a 1/f^2 spectrum with a magnitude attenuated about 75 dB from the no amplification value.
No associations
LandOfFree
Noise Measurements of Yttrium BARIUM(2) COPPER(3) OXYGEN(7) Thin Film High-Temperature Superconductors does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Noise Measurements of Yttrium BARIUM(2) COPPER(3) OXYGEN(7) Thin Film High-Temperature Superconductors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Noise Measurements of Yttrium BARIUM(2) COPPER(3) OXYGEN(7) Thin Film High-Temperature Superconductors will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-939960