37 research outputs found
Formation and control of electron molecules in artificial atoms: Impurity and magnetic-field effects
Interelectron interactions and correlations in quantum dots can lead to
spontaneous symmetry breaking of the self-consistent mean field resulting in
formation of Wigner molecules. With the use of spin-and-space unrestricted
Hartree-Fock (sS-UHF) calculations, such symmetry breaking is discussed for
field-free conditions, as well as under the influence of an external magnetic
field. Using as paradigms impurity-doped (as well as the limiting case of
clean) two-electron quantum dots (which are analogs to helium-like atoms), it
is shown that the interplay between the interelectron repulsion and the
electronic zero-point kinetic energy leads, for a broad range of impurity
parameters, to formation of a singlet ground-state electron molecule,
reminiscent of the molecular picture of doubly-excited helium. Comparative
analysis of the conditional probability distributions for the sS-UHF and the
exact solutions for the ground state of two interacting electrons in a clean
parabolic quantum dot reveals that both of them describe formation of an
electron molecule with similar characteristics. The self-consistent field
associated with the triplet excited state of the two-electron quantum dot
(clean as well as impurity-doped) exhibits symmetry breaking of the Jahn-Teller
type, similar to that underlying formation of nonspherical open-shell nuclei
and metal clusters. Furthermore, impurity and/or magnetic-field effects can be
used to achieve controlled manipulation of the formation and pinning of the
discrete orientations of the Wigner molecules. Impurity effects are futher
illustrated for the case of a quantum dot with more than two electrons.Comment: Latex/Revtex, 10 pages with 4 gif figures. Small changes to explain
the difference between Wigner and Jahn-Teller electron molecules. A complete
version of the paper with high quality figures inside the text is available
at http://shale.physics.gatech.edu/~costas/qdhelium.html For related papers,
see http://www.prism.gatech.edu/~ph274c
The integrated Sachs-Wolfe Effect -- Large Scale Structure Correlation
We discuss the correlation between late-time integrated Sachs-Wolfe (ISW)
effect in the cosmic microwave background (CMB) temperature anisotropies and
the large scale structure of the local universe. This correlation has been
proposed and studied in the literature as a probe of the dark energy and its
physical properties. We consider a variety of large scale structure tracers
suitable for a detection of the ISW effect via a cross-correlation. In addition
to luminous sources, we suggest the use of tracers such as dark matter halos or
galaxy clusters. A suitable catalog of mass selected halos for this purpose can
be constructed with upcoming wide-field lensing and Sunyaev-Zel'dovich (SZ)
effect surveys. With multifrequency data, the presence of the ISW-large scale
structure correlation can also be investigated through a cross-correlation of
the frequency cleaned SZ and CMB maps. While convergence maps constructed from
lensing surveys of the large scale structure via galaxy ellipticities are less
correlated with the ISW effect, lensing potentials that deflect CMB photons are
strongly correlated and allow, probably, the best mechanism to study the
ISW-large scale structure correlation with CMB data alone.Comment: 10 Pages, PRD submitte
Mochras borehole revisited: a new global standard for Early Jurassic earth history
The Early Jurassic epoch was a time of extreme environmental
change: there are well-documented examples of rapid
transitions from cold, or even glacial, climates to super
greenhouse events, the latter characterized worldwide by
hugely enhanced organic carbon burial, multiple large isotopic
anomalies, global sea-level change, and mass extinction
(Price, 1999; Hesselbo et al., 2000; Jenkyns, 2010; Korte
and Hesselbo, 2011). These icehouse–greenhouse events
not only reflect changes in the global climate system but are
also thought to have had significant influence on the evolution
of Jurassic marine biota (e.g. van de Schootbrugge et
al., 2005; Fraguas et al., 2012). Furthermore, the events may
serve as analogues for present-day and future environmental
transitions