125 research outputs found
Use of quantum quenches to probe the equilibrium current patterns of ultracold atoms in an optical lattice
Atomic bosons and fermions in an optical lattice can realize a variety of
interesting condensed matter states that support equilibrium current patterns
in the presence of synthetic magnetic fields or non-abelian gauge fields. As a
route to probing such mass currents, we propose a nonequilibrium quantum quench
of the Hamiltonian that dynamically converts the current patterns into
experimentally measurable real-space density patterns. We illustrate how a
specific such "unidirectional" quench of the optical lattice can be used to
uncover checkerboard and stripe current orders in lattice Bose superfluids and
Fermi gases, as well as chiral edge currents in an integer quantum Hall state.Comment: 5 pages, 4 figures, Slightly revised, to appear in Phys. Rev. A
(Rapid Communication
Near-Infrared MOSFIRE Spectra of Dusty Star-Forming Galaxies at 0.2<z<4
We present near-infrared and optical spectroscopic observations of a sample
of 450m and 850m-selected dusty star-forming galaxies (DSFGs)
identified in a 400 arcmin area in the COSMOS field. Thirty-one sources of
the 102 targets were spectroscopically confirmed at , identified
primarily in the near-infrared with Keck MOSFIRE and some in the optical with
Keck LRIS and DEIMOS. The low rate of confirmation is attributable both to high
rest-frame optical obscuration in our targets and limited sensitivity to
certain redshift ranges. The high-quality photometric redshifts available in
the COSMOS field allow us to test the robustness of photometric redshifts for
DSFGs. We find a subset (11/31%) of DSFGs with inaccurate () or non-existent photometric redshifts; these have very distinct
spectral energy distributions from the remaining DSFGs, suggesting a decoupling
of highly obscured and unobscured components. We present a composite rest-frame
4300--7300\AA\ spectrum for DSFGs, and find evidence of 20030 km s
gas outflows. Nebular line emission for a sub-sample of our detections indicate
that hard ionizing radiation fields are ubiquitous in high-z DSFGs, even more
so than typical mass or UV-selected high-z galaxies. We also confirm the
extreme level of dust obscuration in DSFGs, measuring very high Balmer
decrements, and very high ratios of IR to UV and IR to H luminosities.
This work demonstrates the need to broaden the use of wide bandwidth technology
in the millimeter to the spectroscopic confirmations of large samples of high-z
DSFGs, as the difficulty in confirming such sources at optical/near-infrared
wavelengths is exceedingly challenging given their obscuration.Comment: 14 pages, 13 figures, ApJ accepted. Composite DSFG Halpha spectrum
available at www.as.utexas.edu/~cmcasey/downloads.htm
Kondo effect near the Van Hove singularity in biased bilayer graphene
Magnetic impurity adsorbed on one of the carbon planes of a bilayer graphene
is studied. The formation of the many-body SU(2) and SU(4) resonances close to
the bandgap is analyzed within the mean field Kotliar-Ruckenstein slave boson
approach. Impact of enhanced hybridization and magnetic instability of bilayer
doped near the Van Hove singularity on the screening of magnetic moment is
discussed.Comment: 10 pages, 8 figure
Gauging the mass of metals in the gas phase of galaxies from the Local Universe to the Epoch of Reionization
The chemical enrichment of dust and metals are vital processes in
constraining the star formation history of the universe. Previously, the dust
masses of high-redshift star-forming galaxies have been determined through
their far-infrared continuum, however, equivalent, and potentially simpler,
approaches to determining the metal masses have yet to be explored at . Here, we present a new method of inferring the metal mass in the
interstellar medium (ISM) of galaxies out to , using the
far-infrared [CII]m emission line as a proxy. We calibrated the
[CII]-to- conversion factor based on a benchmark observational
sample at , in addition to gamma-ray burst sightlines at and
cosmological hydrodynamical simulations of galaxies at and
. We found a universal scaling across redshifts of with a 0.4 dex scatter,
which is constant over more than two orders of magnitude in metallicity. We
applied this scaling to recent surveys for [CII] in galaxies at
and determined the fraction of metals retained in the gas-phase ISM, , as a function of redshift showing that an increasing
fraction of metals reside in the ISM of galaxies at higher redshifts. We place
further constraints on the cosmic metal mass density in the ISM () at and , yielding () and
(). These results are consistent with the expected metal
yields from the integrated star formation history at the respective redshifts.
This suggests that the majority of metals produced at are confined
to the ISM of galaxies.Comment: Accepted in A&A, abstract abridge
Electric field control of spins in bilayer graphene: Local moment formation and local moment interactions
We study local moment formation for adatoms on bilayer graphene (BLG) within
a mean-field theory of the Anderson impurity model. The wavefunctions of the
BLG electrons induce strong particle-hole asymmetry and band dependence of the
hybridization, which is shown to result in unusual features in the impurity
model phase diagram. We also study the effect of varying the chemical
potential, as well as varying an electric field perpendicular to the bilayer;
the latter modifies the density of states of electrons in BLG and, more
significantly, shifts the impurity energy. We show that this leads to regimes
in the impurity phase diagram where local moments can be turned on or off by
applying modest external electric fields. Finally, we show that the RKKY
interaction between local moments can be varied by tuning the chemical
potential (as has also been suggested in monolayer graphene) or, more
interestingly, by tuning the electric field so that it induces changes in the
band structure of BLG.Comment: Revised discussion and figures, 17 page
Strain-induced Evolution of Electronic Band Structures in a Twisted Graphene Bilayer
Here we study the evolution of local electronic properties of a twisted
graphene bilayer induced by a strain and a high curvature. The strain and
curvature strongly affect the local band structures of the twisted graphene
bilayer; the energy difference of the two low-energy van Hove singularities
decreases with increasing the lattice deformations and the states condensed
into well-defined pseudo-Landau levels, which mimic the quantization of massive
Dirac fermions in a magnetic field of about 100 T, along a graphene wrinkle.
The joint effect of strain and out-of-plane distortion in the graphene wrinkle
also results in a valley polarization with a significant gap, i.e., the
eight-fold degenerate Landau level at the charge neutrality point is splitted
into two four-fold degenerate quartets polarized on each layer. These results
suggest that strained graphene bilayer could be an ideal platform to realize
the high-temperature zero-field quantum valley Hall effect.Comment: 4 figure
Topological confinement in an antisymmetric potential in bilayer graphene in the presence of a magnetic field
We investigate the effect of an external magnetic field on the carrier states that are localized at a potential kink and a kink-antikink in bilayer graphene. These chiral states are localized at the interface between two potential regions with opposite signs
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