12 research outputs found
Spin dynamics of wave packets evolving with the Dirac Hamiltonian in atoms with high Z
The motion of circular WP for one electron in central Coulomb field with high
Z is calculated. The WP is defined in terms of solutions of the Dirac equation
in order to take into account all possible relevant effects in particular the
spin-orbit potential. A time scale is defined within which spin dynamics must
be taken into account mainly in the atoms with high Z. Within this time scale
there exists a mechanism of collapses and revivals of the spin already shown by
the authors for harmonic oscillator potential and called the 'spin-orbit
pendulum'. However this effect has not the exact periodicity of the simpler
model, but the WP's spatial motion is nevertheless quite similar.Comment: 17 pages, 9 figures, LaTeX2e, uses IOP style files (included). Title
changed, one reference adde
Decoherence of molecular wave packets in an anharmonic potential
The time evolution of anharmonic molecular wave packets is investigated under
the influence of the environment consisting of harmonic oscillators. These
oscillators represent photon or phonon modes and assumed to be in thermal
equilibrium. Our model explicitly incorporates the fact that in the case of a
nonequidistant spectrum the rates of the environment induced transitions are
different for each transition. The nonunitary time evolution is visualized by
the aid of the Wigner function related to the vibrational state of the
molecule. The time scale of decoherence is much shorter than that of
dissipation, and gives rise to states which are mixtures of localized states
along the phase space orbit of the corresponding classical particle. This
behavior is to a large extent independent of the coupling strength, the
temperature of the environment and also of the initial state.Comment: 7 pages, 4 figure
Nanofabrication by magnetic focusing of supersonic beams
We present a new method for nanoscale atom lithography. We propose the use of
a supersonic atomic beam, which provides an extremely high-brightness and cold
source of fast atoms. The atoms are to be focused onto a substrate using a thin
magnetic film, into which apertures with widths on the order of 100 nm have
been etched. Focused spot sizes near or below 10 nm, with focal lengths on the
order of 10 microns, are predicted. This scheme is applicable both to precision
patterning of surfaces with metastable atomic beams and to direct deposition of
material.Comment: 4 pages, 3 figure
Isotopic and spin selectivity of H_2 adsorbed in bundles of carbon nanotubes
Due to its large surface area and strongly attractive potential, a bundle of
carbon nanotubes is an ideal substrate material for gas storage. In addition,
adsorption in nanotubes can be exploited in order to separate the components of
a mixture. In this paper, we investigate the preferential adsorption of D_2
versus H_2(isotope selectivity) and of ortho versus para(spin selectivity)
molecules confined in the one-dimensional grooves and interstitial channels of
carbon nanotube bundles. We perform selectivity calculations in the low
coverage regime, neglecting interactions between adsorbate molecules. We find
substantial spin selectivity for a range of temperatures up to 100 K, and even
greater isotope selectivity for an extended range of temperatures,up to 300 K.
This isotope selectivity is consistent with recent experimental data, which
exhibit a large difference between the isosteric heats of D_2 and H_2 adsorbed
in these bundles.Comment: Paper submitted to Phys.Rev. B; 17 pages, 2 tables, 6 figure