2,560 research outputs found
Rubidium Rydberg macrodimers
We explore long-range interactions between two atoms excited into high
principal quantum number n Rydberg states, and present calculated potential
energy surfaces (PES) for various symmetries of doubly excited ns and np
rubidium atoms. We show that the PES for these symmetries exhibit deep (~GHz)
potential wells, which can support very extended (~micrometers) bound
vibrational states (macrodimers). We present n-scaling relations for both the
depth De of the wells and the equilibrium separations Re of these macrodimers,
and explore their response to small electric fields and stability with respect
to predissociation. Finally, we present a scheme to form and study these
macrodimers via photoassociation, and show how one can probe the various
\ell-character of the potential wells
Complex microwave conductivity of PrCeCuO thin films using a cavity perturbation method
We report a study of the microwave conductivity of electron-doped
PrCeCuO superconducting thin films using a
cavity perturbation technique. The relative frequency shifts obtained for the
samples placed at a maximum electric field location in the cavity are treated
using the high conductivity limit presented recently by Peligrad
Using two resonance modes, TE (16.5 GHz) and TE
(13 GHz) of the same cavity, only one adjustable parameter is needed
to link the frequency shifts of an empty cavity to the ones of a cavity loaded
with a perfect conductor. Moreover, by studying different sample
configurations, we can relate the substrate effects on the frequency shifts to
a scaling factor. These procedures allow us to extract the temperature
dependence of the complex penetration depth and the complex microwave
conductivity of two films with different quality. Our data confirm that all the
physical properties of the superconducting state are consistent with an order
parameter with lines of nodes. Moreover, we demonstrate the high sensitivity of
these properties on the quality of the films
Raman signatures of classical and quantum phases in coupled dots: A theoretical prediction
We study electron molecules in realistic vertically coupled quantum dots in a
strong magnetic field. Computing the energy spectrum, pair correlation
functions, and dynamical form factor as a function of inter-dot coupling via
diagonalization of the many-body Hamiltonian, we identify structural
transitions between different phases, some of which do not have a classical
counterpart. The calculated Raman cross section shows how such phases can be
experimentally singled out.Comment: 9 pages, 2 postscript figures, 1 colour postscript figure, Latex 2e,
Europhysics Letters style and epsfig macros. Submitted to Europhysics Letter
Continuous star cluster formation in the spiral NGC 45
We determined ages for 52 star clusters with masses < 10^6 solar masses in
the low surface brightness spiral galaxy NGC 45. Four of these candidates are
old globular clusters located in the bulge. The remaining ones span a large age
range. The cluster ages suggest a continuous star/cluster formation history
without evidence for bursts, consistent with the galaxy being located in a
relatively unperturbed environment in the outskirts of the Sculptor group.Comment: 4 pages, 3 figures. To appear in "Island Universes - Structure and
Evolution of Disk Galaxies", Terschelling (Netherlands), July 200
Sympathetic and swap cooling of trapped ions by cold atoms in a MOT
A mixed system of cooled and trapped, ions and atoms, paves the way for ion
assisted cold chemistry and novel many body studies. Due to the different
individual trapping mechanisms, trapped atoms are significantly colder than
trapped ions, therefore in the combined system, the strong binary ionatom
interaction results in heat flow from ions to atoms. Conversely, trapped ions
can also get collisionally heated by the cold atoms, making the resulting
equilibrium between ions and atoms intriguing. Here we experimentally
demonstrate, Rubidium ions (Rb) cool in contact with magneto-optically
trapped (MOT) Rb atoms, contrary to the general expectation of ion heating for
equal ion and atom masses. The cooling mechanism is explained theoretically and
substantiated with numerical simulations. The importance of resonant charge
exchange (RCx) collisions, which allows swap cooling of ions with atoms,
wherein a single glancing collision event brings a fast ion to rest, is
discussed.Comment: 10 pages, 3 figure
Structure and Dynamics of the Globular Cluster Palomar 13
We present Keck/DEIMOS spectroscopy and Canada-France-Hawaii Telescope/MegaCam photometry for the Milky Way globular cluster Palomar 13. We triple the number of spectroscopically confirmed members, including many repeat velocity measurements. Palomar 13 is the only known globular cluster with possible evidence for dark matter, based on a Keck/High Resolution Echelle Spectrometer 21 star velocity dispersion of Ď = 2.2 Âą 0.4 km s^(â1). We reproduce this measurement, but demonstrate that it is inflated by unresolved binary stars. For our sample of 61 stars, the velocity dispersion is Ď = 0.7^(+0.6)_(â0.5) km s^(â1). Combining our DEIMOS data with literature values, our final velocity dispersion is Ď = 0.4^(+0.4)_( â0.3) km s^(â1). We determine a spectroscopic metallicity of [Fe/H] = â1.6 Âą 0.1 dex, placing a 1Ď upper limit of Ď_([Fe/H]) ~ 0.2 dex on any internal metallicity spread. We determine Palomar 13's total luminosity to be M_V = â2.8 Âą 0.4, making it among the least luminous known globular clusters. The photometric isophotes are regular out to the half-light radius and mildly irregular outside this radius. The outer surface brightness profile slope is shallower than typical globular clusters (ÎŁ Îą r^Ρ, Ρ = â2.8 Âą 0.3). Thus at large radius, tidal debris is likely affecting the appearance of Palomar 13. Combining our luminosity with the intrinsic velocity dispersion, we find a dynamical mass of M_(1/2) = 1.3^(+2:7)_(â1.3) Ă 10^3 M_â and a mass-to-light ratio of M/L_V = 2.4^(+5.0)_(â2.4) M_â/L_â. Within our measurement errors, the mass-to-light ratio agrees with the theoretical predictions for a single stellar population. We conclude that, while there is some evidence for tidal stripping at large radius, the dynamical mass of Palomar 13 is consistent with its stellar mass and neither significant dark matter, nor extreme tidal heating, is required to explain the cluster dynamics
Macrodimers: ultralong range Rydberg molecules
We study long range interactions between two Rydberg atoms and predict the
existence of ultralong range Rydberg dimers with equilibrium distances of many
thousand Bohr radii. We calculate the dispersion coefficients ,
and for two rubidium atoms in the same excited level , and find
that they scale like , and , respectively. We show that
for certain molecular symmetries, these coefficients lead to long range
potential wells that can support molecular bound levels. Such macrodimers would
be very sensitive to their environment, and could probe weak interactions. We
suggest experiments to detect these macrodimers.Comment: 4 pages, submitted to PR
Structural relaxations in electronically excited poly(para-phenylene)
Structural relaxations in electronically excited poly(para-phenylene) are
studied using many-body perturbation theory and density-functional-theory
methods. A sophisticated description of the electron-hole interaction is
required to describe the energies of the excitonic states, but we show that the
structural relaxations associated with exciton formation can be obtained quite
accurately within a constrained density-functional-theory approach. We find
that the structural relaxations in the low-energy excitonic states extend over
about 8 monomers, leading to an energy reduction of 0.22 eV and a Stokes shift
of 0.40 eV.Comment: 4 pages, 3 figure
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