493 research outputs found
Once more on electromagnetic form factors of nucleons in extended vector meson dominance model
Extended vector meson dominance model, that allows to describe the
electromagnetic form factors of nucleons obeying the asymptotic quark counting
rule prescriptions and contains the minimal number of free parameters, is
presented. We get a reasonable fit of form factors over experimentally
available space-like region of momentum transfer and get also reasonable
results in the time-like region.Comment: 7 pages, 2 figure
Constraints on the relativistic mean field of -isobar in nuclear matter
The effects of the presence of -isobars in nuclear matter are studied
in the framework of relativistic mean-field theory. The existence of stable
nuclei at saturation density imposes constraints on the -isobar
self-energy and thereby on the mean-field coupling constants of the scalar and
vector mesons with -isobars. The range of possible values for the
scalar and vector coupling constants of -isobars with respect to the
nucleon coupling is investigated and compared to recent predictions of QCD
sum-rule calculations.Comment: 8 pages, Latex using Elsevier style, 2 PS figures, minor changes in
revised versio
Splitting between Bright and Dark excitons in Transition Metal Dichalcogenide Monolayers
The optical properties of transition metal dichalcogenide monolayers such as
the two-dimensional semiconductors MoS and WSe are dominated by
excitons, Coulomb bound electron-hole pairs. The light emission yield depends
on whether the electron-hole transitions are optically allowed (bright) or
forbidden (dark). By solving the Bethe Salpeter Equation on top of wave
functions in density functional theory calculations, we determine the sign and
amplitude of the splitting between bright and dark exciton states. We evaluate
the influence of the spin-orbit coupling on the optical spectra and clearly
demonstrate the strong impact of the intra-valley Coulomb exchange term on the
dark-bright exciton fine structure splitting.Comment: 6 pages, 2 figure
Polarization and time-resolved photoluminescence spectroscopy of excitons in MoSe2 monolayers
We investigate valley exciton dynamics in MoSe2 monolayers in polarization-
and time-resolved photoluminescence (PL) spectroscopy at 4K. Following
circularly polarized laser excitation, we record a low circular polarization
degree of the PL of typically . This is about 10 times lower than the
polarization induced under comparable conditions in MoS2 and WSe2 monolayers.
The evolution of the exciton polarization as a function of excitation laser
energy and power is monitored in PL excitation (PLE) experiments. Fast PL
emission times are recorded for both the neutral exciton of ps and for
the charged exciton (trion) of 12 ps.Comment: 4 pages, 3 figure
Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides
We study the neutral exciton energy spectrum fine structure and its spin
dephasing in transition metal dichalcogenides such as MoS. The interaction
of the mechanical exciton with its macroscopic longitudinal electric field is
taken into account. The splitting between the longitudinal and transverse
excitons is calculated by means of the both electrodynamical approach and
perturbation theory. This long-range exciton
exchange interaction can induce valley polarization decay. The estimated
exciton spin dephasing time is in the picosecond range, in agreement with
available experimental data.Comment: 5 pages, 3 figure
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