1,296 research outputs found
Vibrational spectroscopy of H2+: precise evaluation of the Zeeman effect
We present an accurate computation of the g-factors of the hyperfine states
of the hydrogen molecular ion H2+. The results are in good agreement with
previous experiments, and can be tested further by rf spectroscopy. Their
implication for high-precision two-photon vibrational spectroscopy of H2+ is
also discussed. It is found that the most intense hyperfine components of
two-photon lines benefit from a very small Zeeman splitting
Effect of nuclear motion on the critical nuclear charge for two-electron atoms
A variational method for calculating the critical nuclear charge, Zc, required for the binding of a nucleus to two electrons is reported. The method is very effective and performs well compared to the traditional variational principle for calculating energy. The critical nuclear charge, which corresponds to the minimum charge required for the atomic system to have at least one bound state, has been calculated for helium-like systems both with infinite and finite nuclear masses. The value of 0.911 028 2(3) is in very good agreement with recent values in the literature for two-electron atoms with an infinite nuclear mass. When nuclear motion is considered, the value for Zc varies from 0.911 030 3(2) for that with a nuclear mass of Ne (the largest heliogenic system considered) to 0.921 802 4(4) for a system with the nuclear mass of a positron. In all cases the energy varies smoothly as . It is found that for the finite nuclear mass case, in agreement with previous work for the fixed nucleus mass system, the outer electron remains localised near the nucleus at Z = Zc. Additionally, the electron probability distribution is calculated to determine the behaviour of the electrons at low Z
Excitonic Dynamical Franz-Keldysh Effect
The Dynamical Franz-Keldysh Effect is exposed by exploring near-bandgap
absorption in the presence of intense THz electric fields. It bridges the gap
between the DC Franz- Keldysh effect and multi-photon absorption and competes
with the THz AC Stark Effect in shifting the energy of the excitonic resonance.
A theoretical model which includes the strong THz field non-perturbatively via
a non-equilibrium Green Functions technique is able to describe the Dynamical
Franz-Keldysh Effect in the presence of excitonic absorption.Comment: 4 pages in revtex with 5 figures included using epsf. Submitted to
Physical Review Letter
Quasienergy Spectroscopy of Excitons
We theoretically study nonlinear optics of excitons under intense THz
irradiation. In particular, the linear near infrared absorption and resonantly
enhanced nonlinear sideband generation are described. We predict a rich
structure in the spectra which can be interpreted in terms of the quasienergy
spectrum of the exciton, via a remarkably transparent expression for the
susceptibility, and show that the effects of strongly avoided quasienergy
crossings manifest themselves directly, both in the absorption and transmitted
sidebands.Comment: 4 pages RevTex, 3 eps figs included, as publishe
Linear optical absorption spectra of mesoscopic structures in intense THz fields: free particle properties
We theoretically study the effect of THz radiation on the linear optical
absorption spectra of semiconductor structures. A general theoretical
framework, based on non-equilibrium Green functions, is formulated, and applied
to the calculation of linear optical absorption spectrum for several
non-equilibrium mesoscopic structures. We show that a blue-shift occurs and
sidebands appear in bulk-like structures, i.e., the dynamical Franz-Keldysh
effect [A.-P. Jauho and K. Johnsen, Phys. Rev. Lett. 76, 4576 (1996)]. An
analytic calculation leads to the prediction that in the case of superlattices
distinct stable steps appear in the absorption spectrum when conditions for
dynamical localization are met.Comment: 13 Pages, RevTex using epsf to include 8 ps figures. Submitted to
Phys. Rev. B (3 April 97
Interferometric signatures of single molecules
We built an, interferometer where one of the two slits of a classical Young's setup is replaced by a single molecule embedded in a solid matrix. This enabled direct measurement of the first order coherence of the 0-0 single-molecule emission, which at high excitation powers proves to be split in coherent and incoherent parts. We demonstrate an order of magnitude higher precision in axial localization of single molecules in comparison with that of confocal microscopy. These experiments open a possibility for single-molecule holography. Detection of single molecules with low luminescence quantum yields could be another application of this technique
On the Theory of Vibronic Superradiance
The Dicke superradiance on vibronic transitions of impurity crystals is
considered. It is shown that parameters of the superradiance (duration and
intensity of the superradiance pulse and delay times) on each vibronic
transition depend on the strength of coupling of electronic states with the
intramolecular impurity vibration (responsible for the vibronic structure of
the optical spectrum in the form of vibrational replicas of the pure electronic
line) and on the crystal temperature through the Debye-Waller factor of the
lattice vibrations. Theoretical estimates of the ratios of the time delays, as
well as of the superradiance pulse intensities for different vibronic
transitions well agree with the results of experimental observations of
two-color superradiance in the polar dielectric KCl:O2-. In addition, the
theory describes qualitatively correctly the critical temperature dependence of
the superradiance effect.Comment: 8 pages, 1 figur
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Search for anomalous t t-bar production in the highly-boosted all-hadronic final state
A search is presented for a massive particle, generically referred to as a
Z', decaying into a t t-bar pair. The search focuses on Z' resonances that are
sufficiently massive to produce highly Lorentz-boosted top quarks, which yield
collimated decay products that are partially or fully merged into single jets.
The analysis uses new methods to analyze jet substructure, providing
suppression of the non-top multijet backgrounds. The analysis is based on a
data sample of proton-proton collisions at a center-of-mass energy of 7 TeV,
corresponding to an integrated luminosity of 5 inverse femtobarns. Upper limits
in the range of 1 pb are set on the product of the production cross section and
branching fraction for a topcolor Z' modeled for several widths, as well as for
a Randall--Sundrum Kaluza--Klein gluon. In addition, the results constrain any
enhancement in t t-bar production beyond expectations of the standard model for
t t-bar invariant masses larger than 1 TeV.Comment: Submitted to the Journal of High Energy Physics; this version
includes a minor typo correction that will be submitted as an erratu
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