Recent experimental evidence, based on STM studies of BSCCO crystal surface, revealed the presence of nanostructures (nanodomains or stripe-like features) in this material. This raises two important questions: Are the nanostructures universal in high temperature superconductors (HTSC), i.e. are they also present in other HTSC compounds like YBCO and TBCCO? Are the nanostructures present in the bulk of a superconductor, or only on its surface? The presence of nanostructures in a superconductor implies an intrinsic phase separation and consequently a filamentary (percolative) flow of transport current. A superconductor could then behave like a glass with its properties governed by a 2D network of superconducting and normal filaments. We tested these ideas by investigating transport properties of HTSC (YBCO and TBCCO) in the normal and the superconducting states as a function of temperature, and their dependence on the annealing time.
The concept of ferroelasticity and ferroelastic transition is perovskite oxides is reviewed. The presence of ferroelasticity in perovskite cuprates has been revealed by the stress-strain ferroelastic hysteresis, abrupt changes in the temperature dependence of atomic displacements and by formation of ferroelastic domain walls and nanodomains in the copper-oxygen planes. Ferroelastic properties could be responsible for many macroscopic physical properties of HTSC cuprates, including electric transport and magnetic properties, tunneling spectra and phase diagrams.
Correlation between the nanoscopic disorder in the nanostructures in the a-b planes of high Tc superconductors and the macroscopic properties has been studied. It has been found that nanostructures govern the temperature dependence of the transport and magnetic properties such as: the critical current density Jc(T), the superfluid density ns(T)varies direct as1/(lambda) ab2(T) and the normalized magnetic relaxation rate S(T). They also determine magnetic flux pinning: the dependence of the energy barrier on the current density Ueff(J). Irradiation with heavy ions affects the above properties through the change of the disorder in the nanostructure array. The studies have been performed on YBCO and TlBCCO thin films.
KEYWORDS: Information operations, Solids, Thin films, Magnetism, Superconductors, Technetium, Data modeling, Nanostructures, Temperature metrology, Superposition
We have investigated a temperature dependence of the critical current density Jc(T) and a dependence of the energy barrier for vortex motion on current density Ueff(J) in several YBCO and TBCCO thin films. The measurements have been done using rings in a persistent mode and a scanning Hall probe to record Jc(T) and Ueff(J). The results revealed that both quantities exhibit a universal behavior governed by an intrinsic property of these superconductors; Josephson nanostructures in the a-b planes of YBCO and TBCCO.
Th Raman spectrum of YBa2Cu3O7 contains three phonon modes at 502, 435, and
337 cm that arise from the vibrations of oxyn atoms only. These lines are
consequently shifted when 0 is substituted for 0 and the measured shifts can 11e
compared with theoretical1 predictions and used to determine the degree of 0
substitution. The 502 cm phonon, which involves the moti?i of the 0(4) bridging
atoms has been observed to be broadened significantly by 0 substitution. This
broadening has been attributed to disorder induced by incomplete substitution at the
0(4) site. To test this hypothesis the equations of motion for a randomly
substituted linear chain have been solved numerically and the solutions have been
. . . . . 18 used to obtain the linewidth and frequency shift for various degrees of 0
substitution. Good agreement is obtained with the experimental data and the results
are discussed in the context of proosed mechanisms6for oxygen exchange. The
temperature dependence of the 502 cm mode in both 0 samples and 0-exchanged
samples has been carefuly investigated and the measured linewidth has been found to
decrease by about 3 cm at T a1nd then increase again at lower temperatures. The
possible coupling of the 502 cm mode to charge transfer excitations is discussed.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.