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[en] This volume is composed of 51 papers presented at the symposium. Topics covered are: physical properties of oxide superconductors; thin film growth and properties; and device physics and new concepts
[en] This conference was divided into the following sessions: electronic and transport properties; photoemission spectroscopy; Raman spectroscopy; tunneling spectroscopy; photoinduced phenomena; thin-film structures; novel devices; and poster session. Separate abstracts were prepared for 27 papers in this conference
[en] This volume is composed of 26 papers presented at the symposium. Topics covered include the following: high-Tc superlattices: intrinsic and artificial; low-Tc superlattices and multilayers; and theory
[en] Part B is divided into the following sections: (1) tunneling, photoelectron, and other spectra; (2) tunneling spectra: theoretical studies; (3) photoelectron spectra; and (4) other spectra (XAFS, RBS, ESR, Moessbauer, thermoreflectance, etc.). Separate abstracts were prepared for most papers in this volume
[en] During the ten years that followed the discovery of superconductivity above 30 K in lanthanum barium cuprate by Bednorz and Mueller, the condensed matter physics community has been engaged in an unprecedented worldwide effort in materials processing, characterization of physical properties, and theoretical modeling of superconductors. The present conference has brought together a group of researchers who are actively involved in the experimental determination of the physical properties of high-Tc superconductors, the quest for the microscopic mechanism (or mechanisms) of superconductivity, the search for new physical phenomena in these materials, or the search for new classes of superconducting materials. The distinguishing feature and the unifying theme of this conference was the use of spectroscopic techniques as the primary tools in pursuing these goals. Separate abstracts were prepared for 32 papers in this conference
[en] We study the effect of magnetic fields on the resistance R of a superconducting La1.84Sr0.16CuO4 film patterned into a 'double' network comprising nanosized square loops having their vertexes linked by relatively long wires. The results are compared with those obtained in a regular network of square loops of the same size. Both networks exhibit periodic dependence of R on the ratio Φ/Φ0 between the flux penetrating a loop and the superconducting flux quantum. However, while the regular network exhibit features characteristics of collective behavior of the loops, the double network exhibits a single-loop behavior. This observation indicates uncorrelated arrangements of fluxoids in the double network, in agreement with a recent theoretical prediction.
[en] Other than charge carriers, the only low-energy excitations in HTSC materials are phonons and plasmons, but each of these shows some unusual features. Certain phonons are quite polar, strongly coupled to electrons and anharmonic. An unusual Im( - 1/ε proportional to E2 law is attributed to plasmon spectrum being similar to that of the LEG model. Charge carriers are described as highly concentrated intermediate polarons, all of which pair in real space at or close to Tc
[en] A superconducting La1.84Sr0.16CuO4 film patterned into a network of 100 x 100 nm2 noninteracting square loops exhibits large magnetoresistance oscillations superimposed on a background which increases monotonically with the applied magnetic field. Neither the oscillations amplitude nor its temperature dependence can be explained by the Little-Parks effect. Conversely, a good quantitative agreement is obtained with a recently proposed model ascribing the oscillations to the interaction between thermally excited moving vortices and the oscillating persistent currents induced in the loops. Extension of this model, allowing for direct interaction of the vortices and antivortices magnetic moment with the applied field, accounts quantitatively for the monotonic background as well. Analysis of the background indicates that in the patterned film both vortices and antivortices are present at comparable densities. This finding is consistent with the occurrence of Berezinskii-Kosterlitz-Thouless transition in La1.84Sr0.16CuO4 films.
[en] Measurements on nanoscale structures constructed from high-temperature superconductors are expected to shed light on the origin of superconductivity in these materials. To date, loops made from these compounds have had sizes of the order of hundreds of nanometeres. Here, we report the results of measurements on loops of La1.84Sr0.16CuO4, a high-temperature superconductor that loses its resistance to electric currents when cooled below ∼38 K, with dimensions down to tens of nanometres. We observe oscillations in the resistance of the loops as a function of the magnetic flux through the loops. The oscillations have a period of h/2e, and their amplitude is much larger than the amplitude of the resistance oscillations expected from the Little-Parks effect. Moreover, unlike Little-Parks oscillations, which are caused by periodic changes in the superconducting transition temperature, the oscillations we observe are caused by periodic changes in the interaction between thermally excited moving vortices and the oscillating persistent current induced in the loops. However, despite the enhanced amplitude of these oscillations, we have not detected oscillations with a period of h/e, as recently predicted for nanoscale loops of superconductors with d-wave symmetry or with a period of h/4e, as predicted for superconductors that exhibit stripes.
[en] A list of experimental observations (structural, spectroscopical, on transport, isomerization, chemical reactions, etc.) on pristine and doped polyacetylene, (CH)chi, which are not compatible with the accepted planar structures and the current theoretical models of charge transport in (CH)chi, is compiled. It is proposed that (CH)chi is helical and that certain defects (short cis segments) in trans-(CH)chi behave like heavy solitons. These assumptions are shown to resolve all the above paradoxes