209 research outputs found
Nanofabricated media with negative permeability at visible frequencies
We report a nanofabricated medium made of electromagnetically coupled pairs
of gold dots with geometry carefully designed at a 10-nm level. The medium
exhibits strong magnetic response at visible-light frequencies, including bands
with negative \mu. The magnetism arises due to the excitation of quadrupole
plasmon resonances. Our approach shows for the first time the feasibility of
magnetism at optical frequencies and paves a way towards magnetic and
left-handed components for visible optics.Comment: 16 pages, 4 figures. submitted to Nature on 1 April 200
Building surface damage recognition based on synthetic data
To detect surface damage to buildings, it is necessary to involve workers who are at risk of industrial injuries when inspecting hard-to-reach areas of industrialpremises. Attraction of special means, such as aerial platforms, safety systems, etc. increase the financial costs with this approach. The use of unmanned aerial vehicles, coupled withneural network algorithms, can simplify this procedure. Due tothe inaccessibility, the problem of obtaining training data forneural networks arises, which can be solved by synthesizingthem in a virtual environment
Optical models of the molecular atmosphere
The use of optical and laser methods for performing atmospheric investigations has stimulated the development of the optical models of the atmosphere. The principles of constructing the optical models of molecular atmosphere for radiation with different spectral composition (wideband, narrowband, and monochromatic) are considered in the case of linear and nonlinear absorptions. The example of the development of a system which provides for the modeling of the processes of optical-wave energy transfer in the atmosphere is presented. Its physical foundations, structure, programming software, and functioning were considered
Optical absorption and activated transport in polaronic systems
We present exact results for the optical response in the one-dimensional
Holstein model. In particular, by means of a refined kernel polynomial method,
we calculate the ac and dc electrical conductivities at finite temperatures for
a wide parameter range of electron phonon interaction. We analyze the
deviations from the results of standard small polaron theory in the
intermediate coupling regime and discuss non-adiabaticity effects in detail.Comment: 7 pages, 8 figure
Stochastic Green's function approach to disordered systems
Based on distributions of local Green's functions we present a stochastic
approach to disordered systems. Specifically we address Anderson localisation
and cluster effects in binary alloys. Taking Anderson localisation of Holstein
polarons as an example we discuss how this stochastic approach can be used for
the investigation of interacting disordered systems.Comment: 12 pages, 7 figures, conference proceedings: Progress in
Nonequilibrium Green's Functions III, 22-26 August 2005, University of Kiel,
German
Electric Field Effect in Atomically Thin Carbon Films
We report a naturally-occurring two-dimensional material (graphene that can
be viewed as a gigantic flat fullerene molecule, describe its electronic
properties and demonstrate all-metallic field-effect transistor, which uniquely
exhibits ballistic transport at submicron distances even at room temperature
Two Dimensional Electron and Hole Gases at the Surface of Graphite
We report high-quality two-dimensional (2D) electron and hole gases induced
at the surface of graphite by the electric field effect. The 2D carriers reside
within a few near-surface atomic layers and exhibit mobilities up to 15,000 and
60,000 cm2/Vs at room and liquid-helium temperatures, respectively. The
mobilities imply ballistic transport at micron scale. Pronounced Shubnikov-de
Haas oscillations reveal the existence of two types of carries in both 2D
electron and hole gases.Comment: related to cond-mat/0410631 where preliminary data for this
experimental system were reporte
Momentum average approximation for models with boson-modulated hopping: Role of closed loops in the dynamical generation of a finite quasiparticle mass
We generalize the momentum average approximation to study the properties of
single polarons in models with boson affected hopping, where the fermion-boson
scattering depends explicitly on both the fermion's and the boson's momentum.
As a specific example, we investigate the Edwards fermion-boson model in both
one and two dimensions. In one dimension, this allows us to compare our results
with exact diagonalization results, to validate the accuracy of our
approximation. The generalization to two-dimensional lattices allows us to
calculate the polaron's quasiparticle weight and dispersion throughout the
Brillouin zone and to demonstrate the importance of Trugman loops in generating
a finite effective mass even when the free fermion has an infinite mass.Comment: 15 pages, 14 figure
Spatiotemporal evolution of polaronic states in finite quantum systems
We study the quantum dynamics of small polaron formation and polaron
transport through finite quantum structures in the framework of the
one-dimensional Holstein model with site-dependent potentials and interactions.
Combining Lanczos diagonalization with Chebyshev moment expansion of the time
evolution operator, we determine how different initial states, representing
stationary ground states or injected wave packets, after an electron-phonon
interaction quench, develop in real space and time. Thereby, the full quantum
nature and dynamics of electrons and phonons is preserved. We find that the
decay out of the initial state sensitively depends on the energy and momentum
of the incoming particle, the electron-phonon coupling strength, and the phonon
frequency, whereupon bound polaron-phonon excited states may emerge in the
strong-coupling regime. The tunneling of a Holstein polaron through a quantum
wall/dot is generally accompanied by strong phonon number fluctuations due to
phonon emission and re-absorption processes.Comment: 13 pages, 15 figures, final versio
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