8,861 research outputs found
Open charm tomography of cold nuclear matter
We study the relative contribution of partonic sub-processes to D meson
production and D meson-triggered inclusive di-hadrons to lowest order in
perturbative QCD. While gluon fusion dominates the creation of large angle
DD-bar pairs, charm on light parton scattering determines the yield of single
inclusive D mesons. The distinctly different non-perturbative fragmentation of
c quarks into D mesons versus the fragmentation of quarks and gluons into light
hadrons results in a strong transverse momentum dependence of anticharm content
of the away-side charm-triggered jet. In p+A reactions, we calculate and resum
the coherent nuclear-enhanced power corrections from the final state partonic
scattering in the medium. We find that single and double inclusive open charm
production can be suppressed as much as the yield of neutral pions from
dynamical high-twist shadowing. Effects of energy loss in p+A collisions are
also investigated phenomenologically and may lead to significantly weaker
transverse momentum dependence of the nuclear attenuation.Comment: 24 pages, 21 figure
Engineering Time-Reversal Invariant Topological Insulators With Ultra-Cold Atoms
Topological insulators are a broad class of unconventional materials that are
insulating in the interior but conduct along the edges. This edge transport is
topologically protected and dissipationless. Until recently, all existing
topological insulators, known as quantum Hall states, violated time-reversal
symmetry. However, the discovery of the quantum spin Hall effect demonstrated
the existence of novel topological states not rooted in time-reversal
violations. Here, we lay out an experiment to realize time-reversal topological
insulators in ultra-cold atomic gases subjected to synthetic gauge fields in
the near-field of an atom-chip. In particular, we introduce a feasible scheme
to engineer sharp boundaries where the "edge states" are localized. Besides,
this multi-band system has a large parameter space exhibiting a variety of
quantum phase transitions between topological and normal insulating phases. Due
to their unprecedented controllability, cold-atom systems are ideally suited to
realize topological states of matter and drive the development of topological
quantum computing.Comment: 11 pages, 6 figure
Bottom-loading dilution refrigerator with ultra-high vacuum deposition capability
A Kelvinox 400 dilution refrigerator with the ability to load samples onto
the mixing chamber from the bottom of the cryostat has been combined with an
ultrahigh-vacuum (UHV) deposition chamber equipped with molecular beam sources.
The liquid helium cooled sample transfer mechanism is used in a manner that
allows films to be grown on substrates which are kept at temperatures of order
8K with chamber pressures in the 10^-9 to 10^-10 Torr range. This system
facilitates the growth of quench-condensed ultrathin films which must always be
kept below ~ 12K in a UHV environment during and after growth. Measurements can
be made on the films down to millikelvin temperatures and in magnetic fields up
to 15 T.Comment: 10 pages text, 1figur
Characterizing the Hofstadter butterfly's outline with Chern numbers
In this work, we report original properties inherent to independent particles
subjected to a magnetic field by emphasizing the existence of regular
structures in the energy spectrum's outline. We show that this fractal curve,
the well-known Hofstadter butterfly's outline, is associated to a specific
sequence of Chern numbers that correspond to the quantized transverse
conductivity. Indeed the topological invariant that characterizes the
fundamental energy band depicts successive stairways as the magnetic flux
varies. Moreover each stairway is shown to be labeled by another Chern number
which measures the charge transported under displacement of the periodic
potential. We put forward the universal character of these properties by
comparing the results obtained for the square and the honeycomb geometries.Comment: Accepted for publication in J. Phys. B (Jan 2009
Synthetic gauge fields in synthetic dimensions
We describe a simple technique for generating a cold-atom lattice pierced by
a uniform magnetic field. Our method is to extend a one-dimensional optical
lattice into the "dimension" provided by the internal atomic degrees of
freedom, yielding a synthetic 2D lattice. Suitable laser-coupling between these
internal states leads to a uniform magnetic flux within the 2D lattice. We show
that this setup reproduces the main features of magnetic lattice systems, such
as the fractal Hofstadter butterfly spectrum and the chiral edge states of the
associated Chern insulating phases.Comment: 5+4 pages, 5+3 figures, two-column revtex; v2: discussion of role of
interactions added, Fig. 1 reshaped, minor changes, references adde
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