3,449 research outputs found

### Delta-Interference of Two Friedel Resonances

When a single resonator is coupled to a continuous spectrum one obtains a
resonance of finite half-width. Such a resonance is known in many fields of
physics. The Friedel resonance is an example where a d-impurity is dissolved in
a simple metal. If two resonators are coupled to the continuous spectrum the
resonances interfere. For identical coupling and frequencies one obtains two
effective resonances. The effective coupling of one of them to the continuum
can be tuned to zero yielding a delta-like resonance

### Phase transition between d-wave and anisotropic s-wave gaps in high temperature oxides superconductors

We study models for superconductivity with two interactions: $V^>$ due to
antiferromagnetic(AF) fluctuations and $V^<$ due to phonons, in a weak coupling
approach to the high temperature superconductivity. The nature of the two
interactions are considerably different; $V^>$ is positive and sharply peaked
at ($\pm\pi$,$\pm\pi$) while $V^<$ is negative and peaked at ($0,0$) due to
weak phonon screening. We numerically find (a) weak BCS attraction is enough to
have high critical temperature if a van Hove anomaly is at work, (b) $V^>$ (AF)
is important to give d-wave superconductivity, (c) the gap order parameter
$\Delta({\bf k})$ is constant(s-wave) at extremely overdope region and it
changes to anisotropic s-wave as doping is reduced, (d) there exists a first
order phase transition between d-wave and anisotropic s-wave gaps. These
results are qualitatively in agreement with preceding works; they should be
modified in the strongly underdope region by the presence of antiferromagnetic
fluctuations and ensuing AF pseudogap.Comment: 4 pages in RevTex (double column), 4 figure

### A Compact Approximate Solution to the Friedel-Anderson Impuriy Problem

An approximate groundstate of the Anderson-Friedel impurity problem is
presented in a very compact form. It requires solely the optimization of two
localized electron states and consists of four Slater states (Slater
determinants). The resulting singlet ground state energy lies far below the
Anderson mean field solution and agrees well with the numerical results by
Gunnarsson and Schoenhammer, who used an extensive 1/N_{f}-expansion for a spin
1/2 impurity with double occupancy of the impurity level.
PACS: 85.20.Hr, 72.15.R

### Effect of temperature on the electronic instability and the crystalline phase change at low temperature of V3Si type compounds

Equations assuming a Jahn-Teller type effect for the d band electrons in V3Si compounds are given, and the results of free-energy change calculations by using some approximations based on these equations are depicted. The tetragonal structure is converted to cubic as the temperature rises past T sub m which is calculated as 13 K. by the Batterman-Barrett method and is measured to be 20-5 K. Other parameters such as change of C sub p with temperature are predicted better

### Electronic instability and change of crystalline phase in compounds of the V3Si type at low temperature

In V3Si, the V atoms form an array of dense linear chains; a tight-binding approximation in one dimension was used to describe the d electrons. The electronic energy calculated by this method was reduced when the lattice is deformed. This lead to a band type of the Jahn Teller effect, which may explain the cubic to tetragonal transition which was observed at low temperatures. The theory can be extended to other superconductors of the V3X type when X=Ga, Ge, Sn, etcetera, or NB3SN

### Theory of Core-Level Photoemission and the X-ray Edge Singularity Across the Mott Transition

The zero temperature core-level photoemission spectrum is studied across the
metal to Mott insulator transition using dynamical mean-field theory and
Wilson's numerical renormalization group. An asymmetric power-law divergence is
obtained in the metallic phase with an exponent alpha(U,Q)-1 which depends on
the strength of both the Hubbard interaction U and the core-hole potential Q.
For Q <~ U_c/2 alpha decreases with increasing U and vanishes at the transition
(U -> U_c) leading to a symmetric peak in the insulating phase. For Q >~ U_c/2,
alpha remains finite close to the transition, but the integrated intensity of
the power-law vanishes and there is no associated peak in the insulator. The
weight and position of the remaining peaks in the spectra can be understood
within a molecular orbital approach.Comment: 5 pages, 6 figure

### The Friedel oscillations in the presence of transport currents

We investigate the Friedel oscillations in a nanowire coupled to two
macroscopic electrodes of different potentials. We show that the wave-length of
the density oscillations monotonically increases with the bias voltage, whereas
the amplitude and the spatial decay exponent of the oscillations remain intact.
Using the nonequilibrium Keldysh Green functions, we derive an explicit formula
that describes voltage dependence of the wave-length of the Friedel
oscillations.Comment: 5 pages, 3 figures, RevTe

### Autoplot: A browser for scientific data on the web

Autoplot is software developed for the Virtual Observatories in Heliophysics
to provide intelligent and automated plotting capabilities for many typical
data products that are stored in a variety of file formats or databases.
Autoplot has proven to be a flexible tool for exploring, accessing, and viewing
data resources as typically found on the web, usually in the form of a
directory containing data files with multiple parameters contained in each
file. Data from a data source is abstracted into a common internal data model
called QDataSet. Autoplot is built from individually useful components, and can
be extended and reused to create specialized data handling and analysis
applications and is being used in a variety of science visualization and
analysis applications. Although originally developed for viewing
heliophysics-related time series and spectrograms, its flexible and generic
data representation model makes it potentially useful for the Earth sciences.Comment: 16 page

### Self-energy corrections to anisotropic Fermi surfaces

The electron-electron interactions affect the low-energy excitations of an
electronic system and induce deformations of the Fermi surface. These effects
are especially important in anisotropic materials with strong correlations,
such as copper oxides superconductors or ruthenates. Here we analyze the
deformations produced by electronic correlations in the Fermi surface of
anisotropic two-dimensional systems, treating the regular and singular regions
of the Fermi surface on the same footing. Simple analytical expressions are
obtained for the corrections, based on local features of the Fermi surface. It
is shown that, even for weak local interactions, the behavior of the
self-energy is non trivial, showing a momentum dependence and a self-consistent
interplay with the Fermi surface topology. Results are compared to experimental
observations and to other theoretical results.Comment: 13 pages, 10 figure

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