49,209 research outputs found
The quasiparticle band gap in the topological insulator Bi2Te3
We present a theoretical study of dispersion of states which form the bulk
band-gap edges in the three-dimensional topological insulator Bi2Te3. Within
density functional theory, we analyze the effect of atomic positions varying
within the error range of the available experimental data and approximation
chosen for the exchange-correlation functional on the bulk band gap and k-space
location of valence- and conduction-band extrema. For each set of the positions
with different exchange-correlation functionals, we show how many-body
corrections calculated within a one-shot GW approach affect the mentioned
characteristics of electronic structure of Bi2Te3. We thus also illustrate to
what degree the one-shot GW results are sensitive to the reference one-particle
band structure in the case of bismuth telluride. We found that for this
topological insulator the GW corrections enlarge the fundamental band gap and
for certain atomic positions and reference band structure bring its value in
close agreement with experiment.Comment: 12 pages, 6 figures, 5 table
Helioseismology: a fantastic tool to probe the interior of the Sun
Helioseismology, the study of global solar oscillations, has proved to be an
extremely powerful tool for the investigation of the internal structure and
dynamics of the Sun. Studies of time changes in frequency observations of solar
oscillations from helioseismology experiments on Earth and in space have shown,
for example, that the Sun's shape varies over solar cycle timescales. In
particular, far-reaching inferences about the Sun have been obtained by
applying inversion techniques to observations of frequencies of oscillations.
The results, so far, have shown that the solar structure is remarkably close to
the predictions of the standard solar model and, recently, that the
near-surface region can be probed with sufficiently high spatial resolution as
to allow investigations of the equation of state and of the solar envelope
helium abundance. The same helioseismic inversion methods can be applied to the
rotational frequency splittings to deduce with high accuracy the internal
rotation velocity of the Sun, as function of radius and latitude. This also
allows us to study some global astrophysical properties of the Sun, such as the
angular momentum, the grativational quadrupole moment and the effect of
distortion induced on the surface (oblateness). The helioseismic approach and
what we have learnt from it during the last decades about the interior of the
Sun are reviewed here.Comment: 36 page
Non-parametric star formation histories for 5 dwarf spheroidal galaxies of the local group
We use recent HST colour-magnitude diagrams of the resolved stellar
populations of a sample of local dSph galaxies (Carina, LeoI, LeoII, Ursa Minor
and Draco) to infer the star formation histories of these systems, .
Applying a new variational calculus maximum likelihood method which includes a
full Bayesian analysis and allows a non-parametric estimate of the function one
is solving for, we infer the star formation histories of the systems studied.
This method has the advantage of yielding an objective answer, as one need not
assume {\it a priori} the form of the function one is trying to recover. The
results are checked independently using Saha's statistic. The total
luminosities of the systems are used to normalize the results into physical
units and derive SN type II rates. We derive the luminosity weighted mean star
formation history of this sample of galaxies.Comment: 14 pages including 7 figures. Accepted to MNRA
The Lorentz Integral Transform (LIT) method and its applications to perturbation induced reactions
The LIT method has allowed ab initio calculations of electroweak cross
sections in light nuclear systems. This review presents a description of the
method from both a general and a more technical point of view, as well as a
summary of the results obtained by its application. The remarkable features of
the LIT approach, which make it particularly efficient in dealing with a
general reaction involving continuum states, are underlined. Emphasis is given
on the results obtained for electroweak cross sections of few--nucleon systems.
Their implications for the present understanding of microscopic nuclear
dynamics are discussed.Comment: 83 pages, 31 figures. Topical review. Corrected typo
Nuclear shape coexistence : a study of the even-even Hg isotopes using the interacting boson model with configuration mixing
Background: The Po, Pb, Hg, and Pt region is known for the presence of coexisting structures that correspond to different particle-hole configurations in the shell model language or equivalently to nuclear shapes with different deformation.
Purpose: We intend to study the configuration mixing phenomenon in the Hg isotopes and to understand how different observables are influenced by it.
Method: We study in detail a long chain of mercury isotopes, Hg172-200, using the interacting boson model with configuration mixing. The parameters of the Hamiltonians are fixed through a least-squares fit to the known energies and absolute B(E2) transition rates of states up to 3 MeV.
Results: We obtained the IBM-CM Hamiltonians and we calculate excitation energies, B(E2)'s, quadrupole shape invariants, wave functions, isotopic shifts, and mean-field energy surfaces.
Conclusions: We obtain a fairly good agreement with the experimental data for all the studied observables and we conclude that the Hamiltonian and the states we obtain constitute a good approximation to the Hg isotopes
Superconductivity in ferromagnetic metals and in compounds without inversion centre
The symmetry properties and the general overview of the superconductivity
theory in the itinerant ferromagnets and in materials without space parity are
presented. The basic notions of unconventional superconductivity are introduced
in broad context of multiband superconductivity which is inherent property of
ferromagnetic metals or metals without centre of inversion.Comment: 38 pages, no figure
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