14,842 research outputs found
Molecular Fine Structure from Water Window X-rays
Postprint (published version
Fine structure of the 0.7 MeV resonance in the 230Th neutron--induced cross section
The fine structure of the 0.7 MeV resonance in the 230Th neutron-induced
cross section is investigated within the hybrid model. A very good agreement
with experimental data is obtained. It is suggested that fine structure of the
cross section quantify the changes of the intrinsic states of the nucleus
during the disintegration process.Comment: 7 pages, 5 figure
Tuning laser-induced bandgaps in graphene
Could a laser field lead to the much sought-after tunable bandgaps in
graphene? By using Floquet theory combined with Green's functions techniques,
we predict that a laser field in the mid-infrared range can produce observable
bandgaps in the electronic structure of graphene. Furthermore, we show how they
can be tuned by using the laser polarization. Our results could serve as a
guidance to design opto-electronic nano-devices.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter
Inelastic electron backscattering in a generic helical edge channel
We evaluate the low-temperature conductance of a weakly interacting
one-dimensional helical liquid without axial spin symmetry. The lack of that
symmetry allows for inelastic backscattering of a single electron, accompanied
by forward-scattering of another. This joint effect of weak interactions and
potential scattering off impurities results in a temperature-dependent
deviation from the quantized conductance, . In addition,
is sensitive to the position of the Fermi level. We determine
numerically the parameters entering our generic model for the
Bernevig-Hughes-Zhang Hamiltonian of a HgTe/CdTe quantum well in the presence
of Rashba spin-orbit coupling.Comment: 4+ pages, 3 figures, published versio
Non-perturbative laser effects on the electrical properties of graphene nanoribbons
The use of Floquet theory combined with a realistic description of the
electronic structure of illuminated graphene and graphene nanoribbons is
developed to assess the emergence of non-adiabatic and non-perturbative effects
on the electronic properties. Here, we introduce an efficient computational
scheme and illustrate its use by applying it to graphene nanoribbons in the
presence of both linear and circular polarization. The interplay between
confinement due to the finite sample size and laser-induced transitions is
shown to lead to sharp features on the average conductance and density of
states. Particular emphasis is given to the emergence of the bulk limit
response.Comment: 14 pages, 8 figures, to appear in J. Phys.: Condens. Matter, special
issue on "Ultrafast and nonlinear optics in carbon nanomaterials
Laser-induced effects on the electronic features of graphene nanoribbons
We study the interplay between lateral confinement and photon-induced
processes on the electronic properties of illuminated graphene nanoribbons. We
find that by tuning the device setup (edges geometries, ribbon width and
polarization direction), a laser with frequency {\Omega} may either not affect
the electronic structure, or induce bandgaps or depletions at \hbar {\Omega}/2,
and/or at other energies not commensurate with half the photon energy. Similar
features are also observed in the dc conductance, suggesting the use of the
polarization direction to switch on and off the graphene device. Our results
could guide the design of novel types of optoelectronic nano-devices.Comment: 4 pages, 3 figure
Arithmetic complexity via effective names for random sequences
We investigate enumerability properties for classes of sets which permit
recursive, lexicographically increasing approximations, or left-r.e. sets. In
addition to pinpointing the complexity of left-r.e. Martin-L\"{o}f, computably,
Schnorr, and Kurtz random sets, weakly 1-generics and their complementary
classes, we find that there exist characterizations of the third and fourth
levels of the arithmetic hierarchy purely in terms of these notions.
More generally, there exists an equivalence between arithmetic complexity and
existence of numberings for classes of left-r.e. sets with shift-persistent
elements. While some classes (such as Martin-L\"{o}f randoms and Kurtz
non-randoms) have left-r.e. numberings, there is no canonical, or acceptable,
left-r.e. numbering for any class of left-r.e. randoms.
Finally, we note some fundamental differences between left-r.e. numberings
for sets and reals
Attosecond Streaking in the Water Window: A New Regime of Attosecond Pulse Characterization
We report on the first streaking measurement of water-window attosecond
pulses generated via high harmonic generation, driven by sub-2-cycle,
CEP-stable, 1850 nm laser pulses. Both the central photon energy and the energy
bandwidth far exceed what has been demonstrated thus far, warranting the
investigation of the attosecond streaking technique for the soft X-ray regime
and the limits of the FROGCRAB retrieval algorithm under such conditions. We
also discuss the problem of attochirp compensation and issues regarding much
lower photo-ionization cross sections compared with the XUV in addition to the
fact that several shells of target gases are accessed simultaneously. Based on
our investigation, we caution that the vastly different conditions in the soft
X-ray regime warrant a diligent examination of the fidelity of the measurement
and the retrieval procedure.Comment: 14 Pages, 12 figure
Exact models for trimerization and tetramerization in spin chains
We present exact models for an antiferromagnetic S=1 spin chain describing
trimerization as well as for an antiferromagnetic S=3/2 spin chain describing
tetramerization. These models can be seen as generalizations of the
Majumdar-Ghosh model. For both models, we provide a local Hamiltonian and its
exact three- or four-fold degenerate ground state wavefunctions, respectively.
We numerically confirm the validity of both models using exact diagonalization
and discuss the low lying excitations.Comment: 7 pages, 8 figure
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