Search results for "GASES"
showing 10 items of 1098 documents
Landau-Zener Transition for Association of an Atomic Bose-Einstein Condensate With Inter-Particle Elastic Interactions Included
2008
International audience; We study strong coupling limit of the non-linear Landau-Zener transition at coherent photo- and magneto-association of cold atoms, focusing on the role of the elastic interspecies scatterings. Using an exact third-order nonlinear differential equation for the molecular state probability, we develop a nontrivial version of the strained parameter method which enables us to construct a highly accurate and simple analytic approximation describing time dynamics of the coupled atom-molecular system.
Multiple mobile excitons manifested as sidebands in quasi-one-dimensional metallic TaSe3
2020
Charge neutrality and their expected itinerant nature makes excitons potential transmitters of information. However, exciton mobility remains inaccessible to traditional optical experiments that only create and detect excitons with negligible momentum. Here, using angle-resolved photoemission spectroscopy, we detect dispersing excitons in the quasi-one-dimensional metallic trichalcogenide, TaSe3. The low density of conduction electrons and the low dimensionality in TaSe3 combined with a polaronic renormalization of the conduction band and the poorly screened interaction between these polarons and photo-induced valence holes leads to various excitonic bound states that we interpret as intrac…
Mechanism of self-trapped hole motion in corundum crystals
1993
Abstract Atomistic simulations of the self-trapped hole eauilibrium geometry and migration in a pure corundum crystal have been carried out using the semiempirical method of intermedia te neglect of differential overlap and atom-atom potentials, as implemented in the CASCADE code. The activation energies for three different hole-hopping mechanisms are calculated. It is shown that the 60° reorientations of a self-trapped hole and hopping to the nearest O-atom triangle reauire almost the same activation energy, approximately 0.9 eV, which agrees auite well with the experi-mental value for hole migration of 0.7 eV. A new mechanism of small-polaron motion is suggested.
Colloid-polymer mixtures between asymmetric walls: Evidence for an interface localization transition
2007
We demonstrate via computer simulation that mixtures of colloids and polymers confined to thin films have the ability to undergo an interface localization transition. While one wall of the film is assumed to be hard for both particles, at the other wall, an additional repulsive potential acts, but on the colloids only. By varying the strength of this repulsion, a crossover from capillary condensation to interface localization is found. The latter occurs under conditions where in the bulk almost complete phase separation has occurred.
Dipolar and Quadrupolar Freezing in(KBr)1−x(KCN)x
1986
Dipolar and quadrupolar susceptibility measurements are reported for the molecular glass system ${(\mathrm{KBr})}_{1\ensuremath{-}x}{(\mathrm{KCN})}_{x}$ covering a wide range of frequencies. The results allow a direct comparison of the dipolar and quadrupolar anomalies and demonstrate unambiguously that the freezing in of the dipolar and quadrupolar degrees of freedom occurs at different temperatures.
Spin dependence of low energy charge exchange between H 2 + and Na
1987
The difference in charge exchange rate in collisions between spin oriented sodium atoms and H 2 + ions has been measured at an energy of about 1 eV. H 2 + was stored in a Penning trap and polarized by spin exchange with Na beam atoms from a hexapole magnet. The ion loss from the trap due to charge exchange was different as we depolarized the atomic beam. From the data we obtain a ratio of cross sections for singlet and triplet collisionsQ 1/Q 3=1.5±0.2 andQ 3=1.2·10−15 cm2.
Mössbauer Spectroscopic Evidence of Angle-Dependent Intersystem Crossing in LiNbO3:Fe3+
1986
M\"ossbauer emission spectra of LiNb${\mathrm{O}}_{3}$:$^{57}\mathrm{Co}$ single crystals in magnetic fields up to 5 T at 4.2 K show initial populations of the $^{6}A_{1\mathrm{g}}$ Zeeman substates of ${\mathrm{Fe}}^{3+}$ which depend strongly on the angle between the crystallographic $c$ axis and the magnetic field. This is interpreted in terms of a crystal-field effect on excited states which influences the initial populations of the Zeeman sublevels of the $^{6}A_{1\mathrm{g}}$ ground term after the electron-capture decay of $^{57}\mathrm{Co}$. An intersystem crossing process due to orbit-lattice interaction can fairly well explain the angular dependence.
From atomic to molecular Bose-Einstein condensates: a physically realizable term-crossing model for cold atom association
2010
Using an exact third-order NL di®erential equation for the molecular state probability, we develop a variational approach which enables us to construct highly accurate analytic approximations describing time dynamics of the coupled atom-molecular system in each of the interaction regimes. We show that the approximation describing time evolution of the molecular state probability both in the weak interaction limit and in the large detuning regime of the strong interaction limit can be written as a sum of two distinct terms; the ¯rst one, being a solution to a limit ¯rst-order NL equation, e®ectively describes the process of the molecule formation while the second one, being a scaled solution…
Roton-roton crossover in strongly correlated dipolar Bose-nonstnon condensates
2011
We study the pair correlations and excitations of a dipolar Bose gas layer. The anisotropy of the dipole-dipole interaction allows us to tune the strength of pair correlations from strong to weak perpendicular and weak to strong parallel to the layer by increasing the perpendicular trap frequency. This change is accompanied by a roton-roton crossover in the spectrum of collective excitations, from a roton caused by the head-to-tail attraction of dipoles to a roton caused by the side-by-side repulsion, while there is no roton excitation for intermediate trap frequencies. We discuss the nature of these two kinds of rotons and the relation to instabilities of dipolar Bose gases. In both regime…
Dynamics of thermally induced optical nonlinearity in GaSe thin slabs
1996
A study of the nonlinear effects shown by thin slabs of GaSe metaled with Au is presented.