1,824 research outputs found
Faraday Rotation Spectroscopy of Quantum-Dot Quantum Wells
Time-resolved Faraday rotation studies of CdS/CdSe/CdS quantum-dot quantum
wells have recently shown that the Faraday rotation angle exhibits several
well-defined resonances as a function of probe energy close to the absorption
edge. Here, we calculate the Faraday rotation angle from the eigenstates of the
quantum-dot quantum well obtained with k.p theory. We show that the large
number of narrow resonances with comparable spectral weight observed in
experiment is not reproduced by the level scheme of a quantum-dot quantum well
with perfect spherical symmetry. A simple model for broken spherical symmetry
yields results in better qualitative agreement with experiment.Comment: 9 pages, 4 figure
Cosmology with X-ray Cluster Baryons
X-ray cluster measurements interpreted with a universal baryon/gas mass
fraction can theoretically serve as a cosmological distance probe. We examine
issues of cosmological sensitivity for current (e.g. Chandra X-ray Observatory,
XMM-Newton) and next generation (e.g. Con-X, XEUS) observations, along with
systematic uncertainties and biases. To give competitive next generation
constraints on dark energy, we find that systematics will need to be controlled
to better than 1% and any evolution in f_gas (and other cluster gas properties)
must be calibrated so the residual uncertainty is weaker than (1+z)^{0.03}.Comment: 6 pages, 5 figures; v2: 13 pages, substantial elaboration and
reordering, matches JCAP versio
Dynamics and constraints of the Unified Dark Matter flat cosmologies
We study the dynamics of the scalar field FLRW flat cosmological models
within the framework of the Unified Dark Matter (UDM) scenario. In this model
we find that the main cosmological functions such as the scale factor of the
Universe, the scalar field, the Hubble flow and the equation of state parameter
are defined in terms of hyperbolic functions. These analytical solutions can
accommodate an accelerated expansion, equivalent to either the dark energy or
the standard models. Performing a joint likelihood analysis of the
recent supernovae type Ia data and the Baryonic Acoustic Oscillations traced by
the SDSS galaxies, we place tight constraints on the main cosmological
parameters of the UDM cosmological scenario. Finally, we compare the UDM
scenario with various dark energy models namely cosmology, parametric
dark energy model and variable Chaplygin gas. We find that the UDM scalar field
model provides a large and small scale dynamics which are in fair agreement
with the predictions by the above dark energy models although there are some
differences especially at high redshifts.Comment: 11 pages, 7 figures, published in Physical Review D, 78, 083509,
(2008
Exploiting Cross Correlations and Joint Analyses
In this report, we present a wide variety of ways in which information from
multiple probes of dark energy may be combined to obtain additional information
not accessible when they are considered separately. Fundamentally, because all
major probes are affected by the underlying distribution of matter in the
regions studied, there exist covariances between them that can provide
information on cosmology. Combining multiple probes allows for more accurate
(less contaminated by systematics) and more precise (since there is
cosmological information encoded in cross-correlation statistics) measurements
of dark energy. The potential of cross-correlation methods is only beginning to
be realized. By bringing in information from other wavelengths, the
capabilities of the existing probes of dark energy can be enhanced and
systematic effects can be mitigated further. We present a mixture of work in
progress and suggestions for future scientific efforts. Given the scope of
future dark energy experiments, the greatest gains may only be realized with
more coordination and cooperation between multiple project teams; we recommend
that this interchange should begin sooner, rather than later, to maximize
scientific gains.Comment: Report from the "Dark Energy and CMB" working group for the American
Physical Society's Division of Particles and Fields long-term planning
exercise ("Snowmass"
Climatologies at high resolution for the earth's land surface areas
High resolution information of climatic conditions is essential to many application in environmental sciences. Here we present the CHELSA algorithm to downscale temperature and precipitation estimates from the European Centre for Medium-Range Weather Forecast (ECMWF) climatic reanalysis interim (ERA-Interim) to a high resolution of 30 arc sec. The algorithm for temperature is based on a statistical downscaling of atmospheric temperature from the ERA-Interim climatic reanalysis. The precipitation algorithm incorporates orographic predictors such as wind fields, valley exposition, and boundary layer height, and a bias correction using Global Precipitation Climatology Center (GPCC) gridded and Global Historical Climate Network (GHCN) station data. The resulting data consist of a monthly temperature and precipitation climatology for the years 1979-2013. We present a comparison of data derived from the CHELSA algorithm with two other high resolution gridded products with overlapping temporal resolution (Tropical Rain Measuring Mission (TRMM) for precipitation, Moderate Resolution Imaging Spectroradiometer (MODIS) for temperature) and station data from the Global Historical Climate Network (GHCN). We show that the climatological data from CHELSA has a similar accuracy to other products for temperature, but that the predictions of orographic precipitation patterns are both better and at a high spatial resolution
Modeling of Particle Transport, Neutrals and Radiation in Magnetically-Confined Plasmas with Aurora
We present Aurora, an open-source package for particle transport, neutrals
and radiation modeling in magnetic confinement fusion plasmas. Aurora's modern
multi-language interface enables simulations of 1.5D impurity transport within
high-performance computing frameworks, particularly for the inference of
particle transport coefficients. A user-friendly Python library allows simple
interaction with atomic rates from the Atomic Data and Atomic Structure
database as well as other sources. This enables a range of radiation
predictions, both for power balance and spectroscopic analysis. We discuss here
the superstaging approximation for complex ions, as a way to group charge
states and reduce computational cost, demonstrating its wide applicability
within the Aurora forward model and beyond. Aurora also facilitates neutral
particle analysis, both from experimental spectroscopic data and other
simulation codes. Leveraging Aurora's capabilities to interface SOLPS-ITER
results, we demonstrate that charge exchange is unlikely to affect the total
radiated power from the ITER core during high performance operation. Finally,
we describe the ImpRad module in the OMFIT framework, developed to enable
experimental analysis and transport inferences on multiple devices using
Aurora.Comment: 8 pages + references, 5 figure
Growth of High-Mobility Bi2Te2Se Nanoplatelets on hBN Sheets by van der Waals Epitaxy
The electrical detection of the surface states of topological insulators is
strongly impeded by the interference of bulk conduction, which commonly arises
due to pronounced doping associated with the formation of lattice defects. As
exemplified by the topological insulator Bi2Te2Se, we show that via van der
Waals epitaxial growth on thin hBN substrates the structural quality of such
nanoplatelets can be substantially improved. The surface state carrier mobility
of nanoplatelets on hBN is increased by a factor of about 3 compared to
platelets on conventional Si/SiOx substrates, which enables the observation of
well-developed Shubnikov-de Haas oscillations. We furthermore demonstrate the
possibility to effectively tune the Fermi level position in the films with the
aid of a back gate
p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor
Electron pairing in the vast majority of superconductors follows the Bardeen-Cooper-Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a -wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a -wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.The work was funded by the following agencies: Royal Society (‘Superconducting Spintronics’), Leverhulme Trust (IN-2013-033), Schiff Foundation, the EPSRC (EP/N017242/1, EP/G037221/1, EP/K01711X/1, EP/K017144/1, EP/N010345/1, EP/M507799/1, EP/L016087/1), ERC Grant Hetero2D, EU Graphene Flagship, COST Action MP-1201, MSCA-IFEF-ST No. 656485-Spin3, Outstanding Academic Fellows programme at NTNU, Research Council of Norway (205591, 216700 and 24080)
p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor
Electron pairing in the vast majority of superconductors follows the Bardeen–Cooper–Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K
p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor
This is the final version. Available on open access from Nature Research via the DOI in this record.Data availability:
The data set generated and analysed during this study are available for access at http://dx.doi.org/10.17863/CAM.6228Electron pairing in the vast majority of superconductors follows the Bardeen–Cooper–Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.Royal SocietyLeverhulme TrustSchiff FoundationEngineering and Physical Sciences Research Council (EPSRC
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