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in subjects: "Transition Element Compounds 665411* -- Basic Superconductivity Studies-- 1992-"

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Lattice instabilities and structural phase transformations in La sub 2 CuO sub 4 superconductors and insulators

Soft-mode structural phase transformations, common in many perovskite-based materials, are also found in La{sub 2}CuO{sub 4} and structurally related oxides. The resulting phase behavior is rather complex, but is a natural consequence of the degeneracy of the soft phonon order parameters. This paper reviews the structural and lattice-dynamical results and their interpretation based upon mean-field statistical mechanical models.

Date: January 1, 1991

Creator: Axe, J.D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Direct, experimental evidence of the Fermi surface in YBa sub 2 Cu sub 3 O sub 7-x

We report new measurements of the electron-positron momentum spectra of YBa{sub 2}Cu{sub 3}O{sub 7-x} performed with ultra-high statistical precision. These data differ from previous results in two significant respects: They show the D{sub 2} symmetry appropriate for untwinned crystals and, more importantly, they show unmistakable, statistically significant, discontinuities that are evidence of a major Fermi surface section. These results provide a partial answer to a question of special signif… more

Date: April 29, 1991

Creator: Haghighi, H.; Kaiser, J. H.; Rayner, S. L.; West, R. N.; Liu, J. Z.; Shelton, R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Neutron scattering studies of magnetism in the high-Tc materials

In this paper, I shall attempt to review what has been learned about magnetism in the high-{Tc} family of compounds using neutron scattering techniques. Whether or not it is true that magnetic effects are involved in an essential way in the mechanism for superconductivity in these materials (a point which has not yet been firmly established), they offer fascinating examples for the study of magnetism for its own sake, being realizations of spin {1/2} 2D quantum antiferromagnets. Further, the ra… more

Date: January 1, 1990

Creator: Sinha, S.K.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Powder diffraction studies using anomalous dispersion

With the increasing availability and accessibility of high resolution powder diffractometers at many synchrotron radiation sources throughout the world, there is rapidly-growing interest in the exploitation of anomalous dispersion techniques for structural studies of polycrystalline materials. In conjunction with the Rietveld profile method for structure refinement, such studies are especially useful for the determination of the site distributions of two or more atoms which are near neighbors i… more

Date: January 1, 1993

Creator: Cox, D.E. (Brookhaven National Lab., Upton, NY (United States)) & Wilkinson, A.P. (California Univ., Santa Barbara, CA (United States). Dept. of Materials)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Synchrotron studies of narrow band materials

Objective was to determine the single-particle electronic structure of selected narrow band materials in order to understand the relation between their electronic structures and novel low energy properties, such as mixed valence, heavy Fermions, Kondo effect, insulator-metal transitions, non-Fermi liquid behavior, and high-temperature superconductivity. This program supports photoemission spectroscopy (PES) at various synchrotrons. The progress is reported under the following section titles: ZS… more

Date: January 1, 1993

Creator: Allen, J.W.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Effect of spontaneous decay of superconductor quasiparticles in the tunneling density of states

Superconductivity has been successfully described with either the Landau-Ginzburg theory of second order phase transitions or with strong-coupling versions of the original BCS theory for almost fifty years. Recent tunneling and photoemission data on the cuprate oxide superconductors may now provide evidence of corrections to the mean field approximation. It has been shown by Zasadzinski et al. that there is a dip at eV [approx equal] 3[Delta][sub 0] in the SIS tunneling conductance, which is th… more

Date: January 1, 1993

Creator: Coffey, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Muon spin relaxation studies of heavy fermion superconductors

This talk will focus recent developments in our understanding of heavy fermion (HF) superconductors and the role that positive muon spin relaxation ([mu]SR) studies have played in helping to elucidate their properties. As illustrations two systems will be discussed: (1) UPd[sub 2]Al[sub 3], one of the most recently discovered HF superconductors, which also displays coexisting magnetic order and (2) UBe[sub 3] doped with small quantities Of Th substituted for U, which displays an interplay betwe… more

Date: January 1, 1993

Creator: Heffner, R.H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The Local Structure of High-Temperature Superconductors

We show how x-ray absorption fine structure (XAFS) has been successfully used in the determination of the local crystal structure of high-temperature superconductors, with advantages over traditional diffraction techniques. We review the experimental results that yielded the first evidence for an axial-oxygen-centered lattice instability connected with the superconductivity transition. The interpretation of this instability in terms of a dynamical tunneling model suggests the presence of polaro… more

Date: January 1, 1992

Creator: Mustre de Leon, Jose; Conradson, Steven D.; Bishop, Alan R. & Raistrick, Ian D.

Item Type: Article

Partner: UNT Libraries Government Documents Department