11,331 research outputs found
Next-nearest-neighbor Tight-binding Model of Plasmons in Graphene
In this paper we investigate the influence of the next-nearest-neighbor
coupling of tight-binding model of graphene on the spectrum of plasmon
excitations. The nearest-neighbor tight-binding model was previously used to
calculate plasmon spectrum in the next paper [1]. We expand the previous
results of the paper by the next-nearest-neighbor tight-binding model. Both
methods are based on the numerical calculation of the dielectric function of
graphene and loss function. Here we compare plasmon spectrum of the
next-nearest and nearest-neighbor tight-binding models and find differences
between plasmon dispersion of two models.Comment: LaTeX, 4 pages, 4 Fig
Ising instability of a Holstein phonon mode in graphene
We study the thermal distribution of phonons in a graphene sheet. Due to the
two electronic bands there are two out-of-plane phonon modes with respect to
the two sublattices. One of these modes undergoes an Ising transition by
spontaneously breaking the sublattice symmetry. We calculate the critical
point, the renormalization of the phonon frequency and the average lattice
distortion. This transition might be observable in Raman scattering and in
transport properties.Comment: 5 pages, 2 figure
The 1983 Iowa Corn Yield Test Report, District 2
Results of the Iowa Com Yield Test are published to aid Iowa farmers in selecting com varieties. This is the sixty-fourth consecutive year for the test
The 1986 Iowa Corn Yield Test Report, District 2
Results of the Iowa Com Yield Test are published to aid Iowa farmers in selecting com varieties. This is the sixty-sixth consecutive year for the test
Sensitive linear response of an electron-hole superfluid in a periodic potential
We consider excitons in a two-dimensional periodic potential and study the
linear response of the excitonic superfluid to an electromagnetic wave at low
and high densities. It turns out that the static structure factor for small
wavevectors is very sensitive to a change of density and temperature. It is a
consequence of the fact that thermal fluctuations play a crucial role at small
wavevectors, since exchanging the order of the two limits, zero temperature and
vanishing wavevector, leads to different results for the structure factor. This
effect could be used for high accuracy measurements in the superfluid exciton
phase, which might be realized by a gated electron-hole gas. The transition of
the exciton system from the superfluid state to a non-superfluid state and its
manifestation by light scattering are discussed.Comment: 9 pages, 5 figure
Frequency splitting of intervalley phonons in graphene
We study the thermal distribution of intervalley phonons in a graphene sheet.
These phonons have two components with the same frequency. The degeneracy of
the two modes is preserved by weak electron-phonon coupling. A sufficiently
strong electron-phonon coupling, however, can result in a splitting into an
optical and an acoustic phonon branch, which creates a fluctuating gap in the
electronic spectrum. We describe these effects by treating the phonon
distribution within a saddle-point approximation. Fluctuations around the
saddle point indicate a Berezinskii-Kosterlitz-Thouless transition of the
acoustic branch. This transition might be observable in the polarization of
Raman scattered light.Comment: 5 pages, 1 figur
Inelastic scattering of atoms in a double well
We study a mixture of two light spin-1/2 fermionic atoms and two heavy atoms
%in a Mott state in a double well potential. Inelastic scattering processes
between both atomic species excite the heavy atoms and renormalize the
tunneling rate and the interaction of the light atoms (polaron effect). The
effective interaction of the light atoms changes its sign and becomes
attractive for strong inelastic scattering. This is accompanied by a crossing
of the energy levels from singly occupied sites at weak inelastic scattering to
a doubly occupied and an empty site for stronger inelastic scattering. We are
able to identify the polaron effect and the level crossing in the quantum
dynamics.Comment: 12 pages, 9 figure
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