4,246 research outputs found
Spatially resolved quantum plasmon modes in metallic nano-films from first principles
Electron energy loss spectroscopy (EELS) can be used to probe plasmon
excitations in nanostructured materials with atomic-scale spatial resolution.
For structures smaller than a few nanometers quantum effects are expected to be
important, limiting the validity of widely used semi-classical response models.
Here we present a method to identify and compute spatially resolved plasmon
modes from first principles based on a spectral analysis of the dynamical
dielectric function. As an example we calculate the plasmon modes of 0.5-4 nm
thick Na films and find that they can be classified as (conventional) surface
modes, sub-surface modes, and a discrete set of bulk modes resembling standing
waves across the film. We find clear effects of both quantum confinement and
non-local response. The quantum plasmon modes provide an intuitive picture of
collective excitations of confined electron systems and offer a clear
interpretation of spatially resolved EELS spectra.Comment: 7 pages, 7 figure
Plasmons on the edge of MoS2 nanostructures
Using ab initio calculations we predict the existence of one-dimensional
(1D), atomically confined plasmons at the edges of a zigzag MoS2 nanoribbon.
The strongest plasmon originates from a metallic edge state localized on the
sulfur dimers decorating the Mo edge of the ribbon. A detailed analysis of the
dielectric function reveals that the observed deviations from the ideal 1D
plasmon behavior result from single-particle transitions between the metallic
edge state and the valence and conduction bands of the MoS2 sheet. The Mo and S
edges of the ribbon are clearly distinguishable in calculated spatially
resolved electron energy loss spectrum owing to the different plasmonic
properties of the two edges. The edge plasmons could potentially be utilized
for tuning the photocatalytic activity of MoS2 nanoparticles
Nonlocal Damping of Helimagnets in One-Dimensional Interacting Electron Systems
We investigate the magnetization relaxation of a one-dimensional helimagnetic
system coupled to interacting itinerant electrons. The relaxation is assumed to
result from the emission of plasmons, the elementary excitations of the
one-dimensional interacting electron system, caused by slow changes of the
magnetization profile. This dissipation mechanism leads to a highly nonlocal
form of magnetization damping that is strongly dependent on the
electron-electron interaction. Forward scattering processes lead to a spatially
constant damping kernel, while backscattering processes produce a spatially
oscillating contribution. Due to the nonlocal damping, the thermal fluctuations
become spatially correlated over the entire system. We estimate the
characteristic magnetization relaxation times for magnetic quantum wires and
nuclear helimagnets.Comment: Final version accepted by Physical Review
Temperature and light requirements for growth of two diatom species (Bacillariophyceae) isolated from an Arctic macroalga
In the present study, two abundant epiphyticdiatom taxa were isolated from the assimilation hairs ofthe brown macroalga Chordaria flagelliformis collected inthe Arctic Kongsfjorden (Spitsbergen, Norway), establishedas unialgal cultures and their growth rates determinedunder controlled photon fluence rate andtemperature conditions. Using morphological (light andscanning electron microscopy) and SSU rRNA gene databoth isolates (ROS D99 and ROS D125) were identifiedas members of a FragilariaSynedropsis clade. Themolecular data of ROS D99 and ROS D125 were notidentical to any other published sequence. While ROSD99 has been identified as Fragilaria barbararum mainlydue to the SEM characteristics, ROS D125 could not bedefinitely identified although morphological data speakfor Fragilaria striatula. Both diatom species showedsimilar growth rates at all temperatures and photon fluencerates tested. They grew well between 0 and 15Cwithoptimum temperatures of 1214C, but did not survive20C. Therefore, compared to Antarctic diatoms bothtaxa from Kongsfjorden can be characterised as eurythermalorganisms. Increasing photon fluence rates between2 and 15 lmol m2 s1 were accompanied with analmost twofold increase in growth rates, but photon fluencerates >15 lmol m2 s1 did not further enhancegrowth pointing to low light requirements. From thesedata optimum, minimum and maximum photon fluencerates and temperatures for growth can be assessed indicatingthat both diatoms are well acclimated to the fluctuatingenvironmental conditions in the Arctic habitat
Current-induced gap opening in interacting topological insulator surfaces
Two-dimensional topological insulators (TIs) host gapless helical edge states
that are predicted to support a quantized two-terminal conductance.
Quantization is protected by time-reversal symmetry, which forbids elastic
backscattering. Paradoxically, the current-carrying state itself breaks the
time-reversal symmetry that protects it. Here we show that the combination of
electron-electron interactions and momentum-dependent spin polarization in
helical edge states gives rise to feedback through which an applied current
opens a gap in the edge state dispersion, thereby breaking the protection
against elastic backscattering. Current-induced gap opening is manifested via a
nonlinear contribution to the system's characteristic, which persists
down to zero temperature. We discuss prospects for realizations in recently
discovered large bulk band gap TIs, and an analogous current-induced gap
opening mechanism for the surface states of three-dimensional TIs.Comment: 6 pages, 2 figures, published versio
Long-lived non-classical correlations for scalable quantum repeaters at room temperature
Heralded single-photon sources with on-demand readout are promising
candidates for quantum repeaters enabling long-distance quantum communication.
The need for scalability of such systems requires simple experimental
solutions, thus favouring room-temperature systems. For quantum repeater
applications, long delays between heralding and single-photon readout are
crucial. Until now, this has been prevented in room-temperature atomic systems
by fast decoherence due to thermal motion. Here we demonstrate efficient
heralding and readout of single collective excitations created in warm caesium
vapour. Using the principle of motional averaging we achieve a collective
excitation lifetime of ms, two orders of magnitude larger than
previously achieved for single excitations in room-temperature sources. We
experimentally verify non-classicality of the light-matter correlations by
observing a violation of the Cauchy-Schwarz inequality with .
Through spectral and temporal analysis we identify intrinsic four-wave mixing
noise as the main contribution compromising single-photon operation of the
source.Comment: 21 pages total, the first 17 pages are the main article and the
remaining pages are supplemental materia
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