552 research outputs found
Charged-phonon theory and Fano effect in the optical spectroscopy of bilayer graphene
Since their discovery, graphene-based systems represent an exceptional
playground to explore the emergence of peculiar quantum effects. The present
paper focuses on the anomalous appearence of strong infrared phonon resonances
in the optical spectroscopy of bilayer graphene and on their pronounced
Fano-like asymmetry, both tunable in gated devices. By developing a full
microscopic many-body approach for the optical phonon response we explain how
both effects can be quantitatively accounted for by the quantum interference of
electronic and phononic excitations. We show that the phonon modes borrow a
large dipole intensity from the electronic background, the so-called
charged-phonon effect, and at the same time interfer with it, leading to a
typical Fano response. Our approach allows one to disentangle the correct
selection rules that control the relative importance of the two (symmetric and
antisymmetric) relevant phonon modes for different values of the doping and/or
of the gap in bilayer graphene. Finally, we discuss the extension of the same
theoretical scheme to the Raman spectroscopy, to explain the lack of the same
features on the Raman phononic spectra. Besides its remarkable success in
explaining the existing experimental data in graphene-based systems, the
present theoretical approach offers a general scheme for the microscopic
understanding of Fano-like features in a wide variety of other systems.Comment: 16 pages, 11 eps figures, PR
Infrared phonon activity in pristine graphite
We study experimentally and theoretically the Fano-shaped phonon peak at 1590
cm (0.2 eV) in the in-plane optical conductivity of pristine graphite.
We show that the anomalously large spectral weight and the Fano asymmetry of
the peak can be qualitatively accounted for by a charged-phonon theory. A
crucial role in this context is played by the particle-hole asymmetry of the
electronic -bands.Comment: 5 pages, 4 figures, 1 tabl
Stratified dispersive model for material characterization using terahertz time-domain spectroscopy
We propose a novel THz material analysis approach which provides highly
accurate material parameters and can be used for industrial quality control.
The method treats the inspected material within its environment locally as a
stratified system and describes the light-matter interaction of each layer in a
realistic way. The approach is illustrated in the time-domain and
frequency-domain for two potential fields of implementation of THz technology:
quality control of (coated) paper sheets and car paint multilayers, both
measured in humid air.Comment: 4 pages, 4 figure
Landau Damping in a 2D Electron Gas with Imposed Quantum Grid
Dielectric properties of semiconductor substrate with imposed two dimensional
(2D) periodic grid of quantum wires or nanotubes (quantum crossbars, QCB) are
studied. It is shown that a capacitive contact between QCB and semiconductor
substrate does not destroy the Luttinger liquid character of the long wave QCB
excitations. However, the dielectric losses of a substrate surface are
drastically modified due to diffraction processes on the QCB superlattice.
QCB-substrate interaction results in additional Landau damping regions of the
substrate plasmons. Their existence, form and the density of losses are
strongly sensitive to the QCB lattice constant.Comment: 9 pages, 12 eps-figure
A short distance quark-antiquark potential
Leading terms of the static quark-antiquark potential in the background
perturbation theory are reviewed, including perturbative, nonperturbative and
interference ones. The potential is shown to describe lattice data at short
quark-antiquark separations with a good accuracy.Comment: 4 pages, 2 figures, talk at the NPD-2002 Conference, December 2-6,
ITEP, Moscow, references update
Temperature-induced pair correlations in clusters and nuclei
The pair correlations in mesoscopic systems such as -size superconducting
clusters and nuclei are studied at finite temperature for the canonical
ensemble of fermions in model spaces with a fixed particle number: i) a
degenerate spherical shell (strong coupling limit), ii) an equidistantly spaced
deformed shell (weak coupling limit). It is shown that after the destruction of
the pair correlations at T=0 by a strong magnetic field or rapid rotation,
heating can bring them back. This phenomenon is a consequence of the fixed
number of fermions in the canonical ensemble
Atomic Force Analysis of Elastic Deformations of CD
The procedure for the determination of elastic parameters according to reference nanometer lithographic marks by atomic force microscopy on samples with up to microscopic sizes is proposed. Analysis of dynamic changes of elastic characteristics that makes it possible to establish the critical rotation velocity of a CD without plastic deformations has been made.
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