132,007 research outputs found
Doping of graphene by a Au(111) substrate: Calculation strategy within the local density approximation and a semiempirical van der Waals approach
We have performed a density functional study of graphene adsorbed on Au(111)
surface using both a local density approximation and a semiempirical van der
Waals approach proposed by Grimme, known as the DFT-D2 method. Graphene
physisorbed on metal has the linear dispersion preserved in the band-structure,
but the Fermi level of the system is shifted with respect to the conical points
which results in a doping effect. We show that the type and amount of doping
depends not only on the choice of the exchange-correlation functional used in
the calculations, but also on the supercell geometry that models the physical
system. We analyzed how the factors such as the in-plane cell parameter and
interlayer spacing in gold influence the Fermi level shift and we found that
even a small variation in these parameters may cause a transition from p-type
to n-type doping. We have selected a reasonable set of model parameters and
obtained that graphene is either undoped or at most slightly p-type doped on
the clean Au(111) surface, which seems to be in line with experimental
findings. On the other hand, modifications of the substrate lattice may induce
larger doping up to 0.30-0.40 eV depending on the graphene-metal adsorption
distance. The sensitivity of the graphene-gold interface to the structural
parameters may allow to tune doping across the samples which could lead to
possible applications in graphene-based electronic devices. We believe that the
present remarks can be also useful for other studies based on the periodic DFT
Localization of fermionic fields on braneworlds with bulk tachyon matter
Recently, Pal and Skar in [arXiv:hep-th/0701266] proposed a mechanism to
arise the warped braneworld models from bulk tachyon matter, which are endowed
with a thin brane and a thick brane. In this framework, we investigate
localization of fermionic fields on these branes. As in the 1/2 spin case, the
field can be localized on both the thin and thick branes with inclusion of
scalar background. In the 3/2 spin extension, the general supergravity action
coupled to chiral supermultiplets is considered to produce the localization on
both the branes as a result.Comment: 9 pages, no figure
The Spatial-Kinematic Structure of the Region of Massive Star Formation S255N on Various Scales
The results of a detailed analysis of SMA, VLA, and IRAM observations of the
region of massive star formation S255N in CO(2---1), \nh, \nhh, \co and some
other lines is presented. Combining interferometer and single-dish data has
enabled a more detailed investigation of the gas kinematics in the moleclar
core on various spatial scales. There are no signs of rotation or isotropic
compression on the scale of the region as whole. The largest fragments of gas
(0.3 pc) are located near the boundary of the regions of ionized
hydrogen S255 and S257. Some smaller-scale fragments are associated with
protostellar clumps. The kinetic temperatures of these fragments lie in the
range 10---80 K. A circumstellar torus with inner radius R
8000 AU and outer radius R 12 000 AU has been detected around the clump
SMA1. The rotation profile indicates the existence of a central object with
mass 8.5/ sin 2 (i) M . SMA1 is resolved into two clumps,
SMA1---NE and SMA1---SE, whose temperatures are 150 K and 25
K, respectively. To all appearances, the torus is involved in the accretion of
surrounding gas onto the two protostellar clumps
Some aspects of geological information contained in LANDSAT images
The characteristics of MSS images and methods of interpretation are analyzed from a geological point of view. The supportive role of LANDSAT data are illustrated in several examples of surface expressions of geological features, such as synclines and anticlines, spectral characteristics of lithologic units, and circular impact structures
Effect of antimony on the eutectic reaction of heavy section spheroidal graphite castings
There is a strong demand for heavy section castings made of spheroidal graphite with a fully ferritic matrix, e.g. for manufacturing hubs for windmills. Such castings with slow solidification process are prone to graphite degeneration that leads to a dramatic decrease of the mechanical properties of the cast parts. Chunky graphite is certainly the most difficult case of graphite degeneracy, though it has long been known that the limited and controlled addition of antimony may help eliminate it. The drawback of this remedy is that too large Sb additions lead to other forms of degenerate graphite, and also that antimony is a pearlite promoter. As part of an investigation aimed at mastering low level additions to cast iron melts before casting, solidification of large blocks with or without Sb added was followed by thermal analysis. Comparison of the cooling curves and of the microstructures of these different castings gives suggestions to understand the controlling nucleation and growth mechanisms for chunky graphite cells
Decoherence of coupled electron spins via nuclear spin dynamics in quantum dots
In double quantum dots, the exchange interaction between two electron spins
renormalizes the excitation energy of pair-flips in the nuclear spin bath,
which in turn modifies the non-Markovian bath dynamics. As the energy
renormalization varies with the Overhauser field mismatch between the quantum
dots, the electron singlet-triplet decoherence resulting from the bath dynamics
depends on sampling of nuclear spin states from an ensemble, leading to the
transition from exponential decoherence in single-sample dynamics to power-law
decay under ensemble averaging. In contrast, the decoherence of a single
electron spin in one dot is essentially the same for different choices of the
nuclear spin configuration.Comment: 4 pages 3 figure
Multiple Lifshitz transitions driven by short-range antiferromagnetic correlations in the two-dimensional Kondo lattice model
With a mean field approach, the heavy Fermi liquid in the two-dimensional
Kondo lattice model is carefully considered in the presence of short-range
antiferromagnetic correlations. As the ratio of the local Heisenberg
superexchange coupling to the Kondo coupling increases, the Fermi surface
structure changes dramatically. From the analysis of the ground state energy
density, multiple Lifshitz type phase transitions occur at zero temperature.Comment: 4 pages, 3 figures, contribution to SCES201
Visualization of vortex bound states in polarized Fermi gases at unitarity
We analyse theoretically a single vortex in 3D trapped atomic Fermi gases
with population polarization near a broad Feshbach resonance. Above a critical
polarization the Andreev-like bound states inside the core become occupied for
the majority component. As a result, the local density difference at the core
center acquires a sudden rise at low temperautres. This provides a
visualization of the lowest bound state within the absorption imaging
technique. As the polarization increases, the core expands gradually, and
correspondingly, the energy of the lowest bound state decreases.Comment: 4 pages, and 4 figures; Published version in PR
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