2,792 research outputs found
Velocity renormalization and anomalous quasiparticle dispersion in extrinsic graphene
Using many-body diagrammatic perturbation theory we consider carrier density-
and substrate-dependent many-body renormalization of doped or gated graphene
induced by Coulombic electron-electron interaction effects. We quantitatively
calculate the many-body spectral function, the renormalized quasiparticle
energy dispersion, and the renormalized graphene velocity using the
leading-order self-energy in the dynamically screened Coulomb interaction
within the ring diagram approximation. We predict experimentally detectable
many-body signatures, which are enhanced as the carrier density and the
substrate dielectric constant are reduced, finding an intriguing instability in
the graphene excitation spectrum at low wave vectors where interaction
completely destroys all particle-like features of the noninteracting linear
dispersion. We also make experimentally relevant quantitative predictions about
the carrier density and wave-vector dependence of graphene velocity
renormalization induced by electron-electron interaction. We compare on-shell
and off-shell self-energy approximations within the ring diagram approximation,
finding a substantial quantitative difference between their predicted velocity
renormalization corrections in spite of the generally weak-coupling nature of
interaction in graphene.Comment: 9 pages, 6 figure
Ab initio GW electron-electron interaction effects in Quantum Transport
We present an ab initio approach to electronic transport in nanoscale systems
which includes electronic correlations through the GW approximation. With
respect to Landauer approaches based on density-functional theory (DFT), we
introduce a physical quasiparticle electronic-structure into a non-equilibrium
Green's function theory framework. We use an equilibrium non-selfconsistent
self-energy considering both full non-hermiticity and dynamical
effects. The method is applied to a real system, a gold mono-atomic chain. With
respect to DFT results, the conductance profile is modified and reduced by to
the introduction of diffusion and loss-of-coherence effects. The linear
response conductance characteristic appear to be in agreement with experimental
results.Comment: 5 pages, 4 figures, refused by PR
GW method with the self-consistent Sternheimer equation
We propose a novel approach to quasiparticle GW calculations which does not
require the computation of unoccupied electronic states. In our approach the
screened Coulomb interaction is evaluated by solving self-consistent
linear-response Sternheimer equations, and the noninteracting Green's function
is evaluated by solving inhomogeneous linear systems. The frequency-dependence
of the screened Coulomb interaction is explicitly taken into account. In order
to avoid the singularities of the screened Coulomb interaction the calculations
are performed along the imaginary axis, and the results are analytically
continued to the real axis through Pade' approximants. As a proof of concept we
implemented the proposed methodology within the empirical pseudopotential
formalism and we validated our implementation using silicon as a test case. We
examine the advantages and limitations of our method and describe promising
future directions.Comment: 18 pages, 6 figure
Band structures of rare gas solids within the GW approximation
Band structures for solid rare gases (Ne, Ar) have been calculated using the
GW approximation. All electron and pseudopotential ab initio calculations were
performed using Gaussian orbital basis sets and the dependence of particle-hole
gaps and electron affinities on basis set and treatment of core electrons is
investigated. All electron GW calculations have a smaller particle-hole gap
than pseudopotential GW calculations by up to 0.2 eV. Quasiparticle electron
and hole excitation energies, valence band widths and electron affinities are
generally in very good agreement with those derived from optical absorption and
photoemission measurements.Comment: 7 pages 1 figur
A dynamo theory prediction for solar cycle 22: Sunspot number, radio flux, exospheric temperature, and total density at 400 km
Using the dynamo theory method to predict solar activity, a value for the smoothed sunspot number of 109 + or - 20 is obtained for solar cycle 22. The predicted cycle is expected to peak near December, 1990 + or - 1 year. Concommitantly, F(10.7) radio flux is expected to reach a smoothed value of 158 + or - 18 flux units. Global mean exospheric temperature is expected to reach 1060 + or - 50 K and global total average total thermospheric density at 400 km is expected to reach 4.3 x 10 to the -15th gm/cu cm + or - 25 percent
The quasiparticle spectral function in doped graphene
We calculate the real and imaginary electron self-energy as well as the
quasiparticle spectral function in doped graphene taking into account
electron-electron interaction in the leading order dynamically screened Coulomb
coupling. Our theory provides the basis for calculating {\it all} one-electron
properties of extrinsic graphene. Comparison with existing ARPES measurements
shows broad qualitative agreement between theory and experiment. We also
calculate the renormalized graphene momentum distribution function, finding a
typical Fermi liquid discontinuity at k_F. We also provide a critical
discussion of the relevant many body approximations (e.g. RPA) for graphene.Comment: 5 pages, 3 figure
Simulation of neutrino and charged particle production and propagation in the atmosphere
A precise evaluation of the secondary particle production and propagation in
the atmosphere is very important for the atmospheric neutrino oscillation
studies. The issue is addressed with the extension of a previously developed
full 3-Dimensional Monte-Carlo simulation of particle generation and transport
in the atmosphere, to compute the flux of secondary protons, muons and
neutrinos. Recent balloon borne experiments have performed a set of accurate
flux measurements for different particle species at different altitudes in the
atmosphere, which can be used to test the calculations for the atmospheric
neutrino production, and constrain the underlying hadronic models. The
simulation results are reported and compared with the latest flux measurements.
It is shown that the level of precision reached by these experiments could be
used to constrain the nuclear models used in the simulation. The implication of
these results for the atmospheric neutrino flux calculation are discussed.Comment: 11 pages, 9 figure
Empirical wind model for the middle and lower atmosphere. Part 1: Local time average
The HWM90 thermospheric wind model was revised in the lower thermosphere and extended into the mesosphere and lower atmosphere to provide a single analytic model for calculating zonal and meridional wind profiles representative of the climatological average for various geophysical conditions. Gradient winds from CIRA-86 plus rocket soundings, incoherent scatter radar, MF radar, and meteor radar provide the data base and are supplemented by previous data driven model summaries. Low-order spherical harmonics and Fourier series are used to describe the major variations throughout the atmosphere including latitude, annual, semiannual, and longitude (stationary wave 1). The model represents a smoothed compromise between the data sources. Although agreement between various data sources is generally good, some systematic differences are noted, particularly near the mesopause. Root mean square differences between data and model are on the order of 15 m/s in the mesosphere and 10 m/s in the stratosphere for zonal wind, and 10 m/s and 4 m/s, respectively, for meridional wind
GW approximations and vertex corrections on the Keldysh time-loop contour: application for model systems at equilibrium
We provide the formal extension of Hedin's GW equations for single-particle
Green's functions with electron-electron interaction onto the Keldysh time-loop
contour. We show an application of our formalism to the plasmon model of a core
electron within the plasmon-pole approximation. We study in detail the
diagrammatic perturbation expansion of the core-electron/plasmon coupling on
the spectral functions of the so-called S-model which provides an exact
solution, concentrating especially on the effects of self-consistency and
vertex corrections on the GW self-energy. For the S-model, self-consistency is
essential for GW-like calculations to obtain the full spectral information. The
second- order exchange diagram (i.e. a vertex correction) is crucial to obtain
a better spectral description of the plasmon peak and side-band peaks in
comparison to GW-like calculations. However, the vertex corrections are well
reproduced within a non-self-consistent calculation. We also consider
conventional equilibrium GW calculations for the pure jellium model. We find
that with no second-order vertex correction, we cannot obtain the full set of
plasmon side-band peaks. Finally, we address the issues of formal connection
for the Dyson equations of the time-ordered Green's function and the Keldysh
Green's functions at equilibrium in the cases of zero and finite temperature.Comment: Published in PRB November 22 201
Ab initio many-body calculation of excitons in solid Ne and Ar
Absorption spectra, exciton energy levels and wave functions for solid Ne and
Ar have been calculated from first principles using many-body techniques.
Electronic band structures of Ne and Ar were calculated using the GW
approximation. Exciton states were calculated by diagonalizing an exciton
Hamiltonian derived from the particle-hole Green function, whose equation of
motion is the Bethe-Salpeter equation. Singlet and triplet exciton series up to
n=5 for Ne and n=3 for Ar were obtained. Binding energies and
longitudinal-transverse splittings of n=1 excitons are in excellent agreement
with experiment. Plots of correlated electron-hole wave functions show that the
electron-hole complex is delocalised over roughly 7 a.u. in solid Ar.Comment: 6 page
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