8,156 research outputs found
Domains of doping in graphene on polycrystalline gold: first-principles and scanning tunneling spectroscopy studies
We have studied the graphene/gold interface by means of density functional
theory (DFT) and scanning tunneling spectroscopy (STS). Weak interaction
between graphene and the underlying gold surface leaves unperturbed Dirac cones
in the band-structure, but they can be shifted with respect to the Fermi level
of the whole system, which results in effective doping of graphene. DFT
calculations revealed that the interface is extremely sensitive to the
adsorption distance and to the structure of metal's surface, in particular
strong variation in doping can be attributed to the specific rearrangements of
substrate's atoms, such as the change in the crystallographic orientation,
relaxation or other modifications of the surface. On the other hand, STS
experiments have shown the presence of energetic heterogeneity in terms of the
changes in the local density of states (LDOS) measured at different places on
the sample. Randomly repeated regions of zero-doping and p-type doping have
been identified from parabolic shape characteristics and from well defined
Dirac points, respectively. The doping domains of graphene on gold seem to be
related to the presence of various types of the surface structure across the
sample. DFT simulations for graphene interacting with Au have shown large
differences in doping induced by considered structures of substrate, in
agreement with experimental findings. All these results demonstrate the
possibility of engineering the electronic properties of graphene, especially
tuning the doping across one flake which can be useful for applications of
graphene in electronic devices
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
An improved single particle potential for transport model simulations of nuclear reactions induced by rare isotope beams
Taking into account more accurately the isospin dependence of nucleon-nucleon
interactions in the in-medium many-body force term of the Gogny effective
interaction, new expressions for the single nucleon potential and the symmetry
energy are derived. Effects of both the spin(isospin) and the density
dependence of nuclear effective interactions on the symmetry potential and the
symmetry energy are examined. It is shown that they both play a crucial role in
determining the symmetry potential and the symmetry energy at supra-saturation
densities. The improved single nucleon potential will be useful for simulating
more accurately nuclear reactions induced by rare isotope beams within
transport models.Comment: 6 pages including 6 figures
On Spinors Transformations
We begin showing that for even dimensional vector spaces all
automorphisms of their Clifford algebras are inner. So all orthogonal
transformations of are restrictions to of inner automorphisms of the
algebra. Thus under orthogonal transformations and - space and time
reversal - all algebra elements, including vectors and spinors ,
transform as and for some
algebra element . We show that while under combined spinor remain in its spinor space, under or separately
goes to a 'different' spinor space and may have opposite chirality.
We conclude with a preliminary characterization of inner automorphisms with
respect to their property to change, or not, spinor spaces.Comment: Minor changes to propositions 1 and
Observation of the fine structure for rovibronic spectral lines in visible part of emission spectra of
For the first time in visible part of the emission spectrum the pseudo
doublets representing partly resolved fine structure of rovibronic lines have
been observed. They are characterized by splitting values about 0.2 cm
and relative intensity of the doublet components close to 2.0. It is shown that
they are determined by triplet splitting in lower rovibronic levels of various
electronic transitions. It is proposed to use
an existence of such partly resolved fine structure patterns for identification
of numerous unassigned spectral lines of the molecule coming from great
variety of triplet "gerade" electronic states to vibro-rotational levels of the
state.Comment: 6 pages, including 2 figures and 1 table; submitted to Phys.Rev.Let
Linear rigidity of stationary stochastic processes
We consider stationary stochastic processes X n , n â Z such that X 0 lies in the closed linear span of X n , n = 0; following Ghosh and Peres, we call such processes linearly rigid. Using a criterion of Kolmogorov, we show that it suffices, for a stationary stochastic process to be rigid, that the spectral density vanish at zero and belong to the Zygmund class Î * (1). We next give sufficient condition for stationary determinantal point processes on Z and on R to be rigid. Finally, we show that the determinantal point process on R 2 induced by a tensor square of Dyson sine-kernels is not linearly rigid
Spin polarized states in neutron matter at a strong magnetic field
Spin polarized states in neutron matter at a strong magnetic field are
considered in the model with the Skyrme effective interaction (SLy4, SLy7
parametrizations). Analyzing the self-consistent equations at zero temperature,
it is shown that a thermodynamically stable branch of solutions for the spin
polarization parameter as a function of density corresponds to the negative
spin polarization when the majority of neutron spins are oriented oppositely to
the direction of the magnetic field. Besides, beginning from some threshold
density being dependent on the magnetic field strength the self-consistent
equations have also two other branches (upper and lower) of solutions for the
spin polarization parameter with the positive spin polarization.
The free energy corresponding to the upper branch turns out to be very close
to the free energy corresponding to the thermodynamically preferable branch
with the negative spin polarization. As a consequence, at a strong magnetic
field, the state with the positive spin polarization can be realized as a
metastable state at the high density region in neutron matter which under
decreasing density at some threshold density changes into a thermodynamically
stable state with the negative spin polarization. The calculations of the
neutron spin polarization parameter and energy per neutron as functions of the
magnetic field strength show that the influence of the magnetic field remains
small at the field strengths up to G.Comment: Prepared with RevTeX4, 8pp., 5 figs; v.2: matches published versio
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