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Spatially-resolved NMR is used to probe antiferromagnetism in the vortex state of nearly optimally doped high- cuprate TlBaCuO ( = 85 K). The broadened Tl-spectra below 20 K and the temperature dependence of the enhanced nuclear spin-lattice relaxation rate at the vortex core region indicate clear evidences of the antiferromagnetic order inside the vortex core of TlBaCuO.

We demonstrate the use of a high-resolution solid-state fast (45 kHz) magic angle spinning (MAS) NMR for mapping the oxygen distribution in Hg-based cuprate superconductors. We identify observed three peaks in Hg spectrum as belonging to the different chemical environments in the HgO layer with no oxygen neighbors, single oxygen neighbor, and two oxygen neighbors. We discuss observed differences between Hg-1201 and Hg-1223 materials.

Thermoelectric power (TEP) of high- superconductors has been investigated in a wide range of temperature ( < < 700 K) for LaSrCuO. For wide doping level from underdoping to heavily overdoping, TEP follows the linear- dependence above the broad peak temperature, . At high temperatures, however, TEP shows deviation from the linear- dependence at a certain temperature , which is consistent with the pseudogap temperature. The systematic change of the TEP behavior is discussed in terms of the two fluids model of bound pairs and independent normal carriers.

Variation of the magnitude and the temperature dependence of the normal state resistivity () has been very frequently observed in different (YBCO) single crystals (or YBCO thin films) of the same . We investigated the origin of these changes by analyzing optimally doped and underdoped YBCO thin films (with 7− = 6.80−6.95) whose resistivity () was characterized by a “superlinear” temperature dependence [with a flattening of () below 230K]. We induced oxygen redistribution in these films without any change in the total oxygen content, by either careful annealing over a temperature range of 120–140° in argon, or by aging at room temperature in air. This procedure leads to a transition from a superlinear () towards the linear one, and an increase of both the magnitude of resistivity and . Long-term aging yields a perfectly linear (). We proposed a filamentary model of the changes in (), which is based on a thermally activated redistribution of the interchain bridging oxygen O(5) in the chain-layer of YBCO. The results show that a perfectly linear () can be observed in YBCO of oxygen content 7− as low as 6.8, which is essential for the development of theories of the normal state resistivity and the pseudo-gap state.

We will summarize here some of our measurements of the superconducting fluctuations effects on the in-plane electrical resistivity (the so-called in-plane paraconductivity) in LaSrCuO thin films with different Sr content. Our results suggest that these superconducting fluctuations effects are not related to the opening of a pseudogap in the normal-state of underdoped compounds.

On the basis of the thermodynamic analysis of the related experimental data, a possibility is shown of a manifestation of a phase fluctuation-like effect in the high-temperature superconducting (HTSC) cuprates, especially with respect to physical properties of melt-textured composites, thin films, coatings, nanomaterials and heterostructures.

I review some of the experimental evidence and theoretical arguments that suggest that pseudogap matter is a new form of matter that coexists with coherent electron matter in the normal state and with superconducting matter below the superconducting transition temperature. I describe work in progress on a phenomenological two-fluid description of the evolution of pseudogap behavior that offers an explanation for the unexpectedly simple scaling behavior for the uniform magnetic susceptibility found in the underdoped cuprates and use this to propose a physical picture of the underdoped cuprates and to estimate the fraction of quasiparticles that become superconducting in underdoped superconductors.

The claims made for the Resonating Valence Bond ideas for the Cuprates in a recent paper by Anderson et al. on the basis of a variational calculation are discussed.

Many apparently unrelated systems, including disordered metals and metallic oxides, undergo a metal/insulator transition (MIT) when their carrier concentrations are reduced and/or their disorder is increased. We have found that the superconducting transition temperature, T, of such materials is very often enhanced in the vicinity of the MIT. We have constructed superconductivity phase diagrams (T vs σ, the conductivity) for many materials whose only common feature is proximity to the MIT and found that they are remarkably similar.

While the majority opinion in the field of high-temperature superconductivity has been that the electron-phonon coupling is irrelevant to the mechanism of superconductivity, recent experimental results suggest otherwise. We show that in the cuprates the electron-phonon coupling is unconventional, and suggest that the Cu-O bond-stretching LO phonons may play a crucial role in superconductivity through formation of a vibronic bound state.