11 research outputs found
Feedback effects and the self-consistent Thouless criterion of the attractive Hubbard model
We propose a fully microscopic theory of the anomalous normal state of the
attractive Hubbard model in the low-density limit that accounts for propagator
renormalization. Our analytical conclusions, which focus on the thermodynamic
instabilities contained in the self-consistent equations associated with our
formulation, have been verified by our comprehensive numerical study of the
same equations. The resulting theory is found to contain no transitions at
non-zero temperatures for all finite lattices, and we have confirmed, using our
numerical studies, that this behaviour persists in the thermodynamic limit for
low-dimensional systems.Comment: 6 pages, 2 eps format figure
The Isotope Effect in d-Wave Superconductors
Based on recently proposed anti-ferromagnetic spin fluctuation exchange
models for -superconductors, we show that coupling to harmonic
phonons {\it{cannot}} account for the observed isotope effect in the cuprate
high- materials, whereas coupling to strongly anharmonic multiple-well
lattice tunneling modes {\it{can}}. Our results thus point towards a strongly
enhanced {\it{effective}} electron-phonon coupling and a possible break-down of
Migdal-Eliashberg theory in the cuprates.Comment: 12 pages + 2 figures, Postscript files, all uuencoded Phys. Rev.
Lett. (1995, to be published
Effect of an Electron-phonon Interaction on the One-electron Spectral Weight of a d-wave Superconductor
We analyze the effects of an electron-phonon interaction on the one-electron
spectral weight A(k,omega) of a d_{x^2-y^2} superconductor. We study the case
of an Einstein phonon mode with various momentum-dependent electron-phonon
couplings and compare the structure produced in A(k,omega) with that obtained
from coupling to the magnetic pi-resonant mode. We find that if the strength of
the interactions are adjusted to give the same renormalization at the nodal
point, the differences in A(k,omega) are generally small but possibly
observable near k=(pi,0).Comment: 10 pages, 14 figures (color versions of Figs. 2,4,10,11,12 available
upon request
Standing laparoscopic herniorrhaphy in stallions using cylindrical polypropylene mesh prosthesis
Tumor-initiating ability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and arochlor 1254 in the two-stage system of mouse skin carcinogenesis
Congenital Erythropoietic Porphyria: Prolonged High-Level Expression and Correction of the Heme Biosynthetic Defect by Retroviral-Mediated Gene Transfer into Porphyric and Erythroid Cells
Magnetic state of Yb in Kondo-lattice YbNi<sub>2</sub>B<sub>2</sub>C
We report neutron scattering experiments performed to investigate the dynamic
magnetic properties of the Kondo-lattice compound YbNi2B2C. The spectrum of
magnetic excitations is found to be broad, extending up to at least 150 meV,
and contains inelastic peaks centred near 18 meV and 43 meV. At low energies we
observe quasielastic scattering with a width Gamma = 2.1 meV. The results
suggest a Yb3+ ground state with predominantly localized 4f electrons subject
to (i) a crystalline electric field (CEF) potential, and (ii) a Kondo
interaction, which at low temperatures is about an order of magnitude smaller
than the CEF interaction. From an analysis of the dynamic magnetic response we
conclude that the crystalline electric field acting on the Yb ions has a
similar anisotropy to that in other RNi2B2C compounds, but is uniformly
enhanced by almost a factor of 2. The static and dynamic magnetic properties of
YbNi2B2C are found to be reconciled quite well by means of an approximation
scheme to the Anderson impurity model, and this procedure also indicates that
the effective Kondo interaction varies with temperature due to the crystal
field splitting. We discuss the nature of the correlated-electron ground state
of YbNi2B2C based on these and other experimental results, and suggest that
this compound might be close to a quantum critical point on the non-magnetic
side.Comment: Revised version to be published in Phys Rev