2,409 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
Electron self-energy in A3C60 (A=K, Rb): Effects of t1u plasmon in GW approximation
The electron self-energy of the t1u states in A3C60 (A=K, Rb) is calculated
using the so-called GW approximation. The calculation is performed within a
model which considers the t1u charge carrier plasmon at 0.5 eV and takes into
account scattering of the electrons within the t1u band. A moderate reduction
(35 %) of the t1u band width is obtained.Comment: 4 pages, revtex, 1 figure more information at
http://www.mpi-stuttgart.mpg.de/dokumente/andersen/fullerene
Renormalization of Molecular Electronic Levels at Metal-Molecule Interfaces
The electronic structure of benzene on graphite (0001) is computed using the
GW approximation for the electron self-energy. The benzene quasiparticle energy
gap is predicted to be 7.2 eV on graphite, substantially reduced from its
calculated gas-phase value of 10.5 eV. This decrease is caused by a change in
electronic correlation energy, an effect completely absent from the
corresponding Kohn-Sham gap. For weakly-coupled molecules, this correlation
energy change is seen to be well described by a surface polarization effect. A
classical image potential model illustrates trends for other conjugated
molecules on graphite.Comment: 4 pages, 3 figures, 2 table
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
The Band-Gap Problem in Semiconductors Revisited: Effects of Core States and Many-Body Self-Consistency
A novel picture of the quasiparticle (QP) gap in prototype semiconductors Si
and Ge emerges from an analysis based on all-electron, self-consistent, GW
calculations. The deep-core electrons are shown to play a key role via the
exchange diagram --if this effect is neglected, Si becomes a semimetal.
Contrary to current lore, the Ge 3d semicore states (e.g., their polarization)
have no impact on the GW gap. Self-consistency improves the calculated gaps --a
first clear-cut success story for the Baym-Kadanoff method in the study of
real-materials spectroscopy; it also has a significant impact on the QP
lifetimes. Our results embody a new paradigm for ab initio QP theory
Neutral winds derived from IRI parameters and from the HWM87 wind model for the sundial campaign of September, 1986
Meridional neutral winds derived from the height of the maximum ionization of the F2 layer are compared with values from results of the HWM87 empirical neutral wind model. The time period considered is the SUNDIAL-2 campaign, 21 Sept. through 5 Oct. 1986. Winds were derived from measurements by a global network of ionosondes, as well as from similar quantities generated by the International Reference Ionosphere. Global wind patterns from the three sources are similar. Differences tend to be the result of local or transient phenomena that are either too rapid to be described by the order of harmonics of the empirical models, or are the result of temporal changes not reproduced by models based on average conditions
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
Fluctuations of g-factors in metal nanoparticles: Effects of electron-electron interaction and spin-orbit scattering
We investigate the combined effect of spin-orbit scattering and
electron-electron interactions on the probability distribution of -factors
of metal nanoparticles. Using random matrix theory, we find that even a
relatively small interaction strength %(ratio of exchange constant and mean
level %spacing \spacing ) significantly increases -factor
fluctuations for not-too-strong spin-orbit scattering (ratio of spin-orbit rate
and single-electron level spacing 1/\tau_{\rm so} \spacing \lesssim 1), and
leads to the possibility to observe -factors larger than two.Comment: RevTex, 2 figures inserte
Violation of particle number conservation in the it GW approximation
We present a nontrivial model system of interacting electrons that can be solved analytically in the GW approximation. We obtain the particle number from the GW Green's function strictly analytically, and prove that there is a genuine violation of particle number conservation if the self-energy is calculated non-self-consistently from a zeroth order Green's function, as done in virtually all practical implementations. We also show that a simple shift of the self-energy that partially restores self-consistency reduces the numerical deviation significantly
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