19,303 research outputs found
Superconductivity in Inhomogeneous Hubbard Models
We present a controlled perturbative approach to the low temperature phase
diagram of highly inhomogeneous Hubbard models in the limit of small coupling,
, between clusters. We apply this to the dimerized and checkerboard models.
The dimerized model is found to behave like a doped semiconductor, with a
Fermi-liquid groundstate with parameters ({\it e.g.} the effective mass) which
are smooth functions of the Hubbard interaction, . By contrast, the
checkerboard model has a nodeless d-wave superconducting state (preformed pair
condensate, -BEC) for , which smoothly crosses over to an
intermediate BCS-like superconducting phase (-BCS), also with no nodal
quasi-particles, for , which gives way to a
Fermi liquid phase at large .Comment: 7 pages, a sign error in Eq.(3) has been corrected and its
consequence has been discussed with updated figure
Optical Spectroscopic Survey of High-latitude WISE-selected Sources
We report on the results of an optical spectroscopic survey at high Galactic latitude (|b| ≥ 30°) of a sample of WISE-selected targets, grouped by WISE W1 (λ_eff = 3.4 μm) flux, which we use to characterize the sources WISE detected. We observed 762 targets in 10 disjoint fields centered on ultraluminous infrared galaxy candidates using DEIMOS on Keck II. We find 0.30 ± 0.02 galaxies arcmin–2 with a median redshift of z = 0.33 ± 0.01 for the sample with W1 ≥ 120 μJy. The foreground stellar densities in our survey range from 0.23 ± 0.07 arcmin–2 to 1.1 ± 0.1 arcmin–2 for the same sample. We obtained spectra that produced science grade redshifts for ≥90% of our targets for sources with W1 flux ≥120 μJy that also had an i-band flux gsim 18 μJy. We used this for targeting very preliminary data reductions available to the team in 2010 August. Our results therefore present a conservative estimate of what is possible to achieve using WISE's Preliminary Data Release for the study of field galaxies
Spontaneous Crystallization of Skyrmions and Fractional Vortices in the Fast-rotating and Rapidly-quenched Spin-1 Bose-Einstein Condensates
We investigate the spontaneous generation of crystallized topological defects
via the combining effects of fast rotation and rapid thermal quench on the
spin-1 Bose-Einstein condensates. By solving the stochastic projected
Gross-Pitaevskii equation, we show that, when the system reaches equilibrium, a
hexagonal lattice of skyrmions, and a square lattice of half-quantized vortices
can be formed in a ferromagnetic and antiferromagnetic spinor BEC, respetively,
which can be imaged by using the polarization-dependent phase-contrast method
Self-energy corrections to anisotropic Fermi surfaces
The electron-electron interactions affect the low-energy excitations of an
electronic system and induce deformations of the Fermi surface. These effects
are especially important in anisotropic materials with strong correlations,
such as copper oxides superconductors or ruthenates. Here we analyze the
deformations produced by electronic correlations in the Fermi surface of
anisotropic two-dimensional systems, treating the regular and singular regions
of the Fermi surface on the same footing. Simple analytical expressions are
obtained for the corrections, based on local features of the Fermi surface. It
is shown that, even for weak local interactions, the behavior of the
self-energy is non trivial, showing a momentum dependence and a self-consistent
interplay with the Fermi surface topology. Results are compared to experimental
observations and to other theoretical results.Comment: 13 pages, 10 figure
Anomalous magnetic moment in parity-conserving QED3
In this article we derive the anomalous magnetic moment of fermions in
(2+1)-dimensional parity-conserving QED3, in the presence of an externally
applied constant magnetic field. We use a spectral representation of the photon
propagator to avoid infrared divergences. We also discuss the scaling with the
magnetic field intensity in the case of strong external fields, where there is
dynamical mass generation for fermions induced by the magnetic field itself
(magnetic catalysis). The results of this paper may be of relevance to the
physics of high-temperature superconductors.Comment: 27 pages LATEX, three eps figures incorporate
Diffuse Axonal Injury: A Devastating Pathology
Traumatic brain injury (TBI) also known as intracranial injury is the result of a lesion within the brain due to an external force. Common forms of TBI result from falls, violence, and/or vehicle crashes; the classification of this pathology is dependent on the severity of the lesion as well as the mechanism of trauma to the head. One of the most common onsets of traumatic brain injuries result from mild to severe lesions to the white matter tracts of the brain called diffuse axonal injury (DAI); however, additional forms of TBI’s can present in non-penetrating forms. Penetrating forms of TBI’s such as trauma to the head via a foreign object do also contribute to the many millions of TBI cases per year, but we will not discuss these traumatic injuries as in depth within this chapter. The onset of diffuse axonal injury will vary on a per-patient basis from mild to severe, based on a standardized neurological examination rated on the Glasgow Coma Scale (GCS), which indicates the severity of brain damage present. While there is a spectrum of severity for DAI patients, a concussion is typically observed within a larger majority of patients in addition to other overwhelming trauma
Metamaterials: optical activity without chirality
We report that the classical phenomenon of optical activity, which is traditionally associated with chirality (helicity) of organic molecules, proteins, and inorganic structures, can be observed in artificial planar media which exhibit neither 3D nor 2D chirality. We observe the effect in the microwave and optical parts of the spectrum at oblique incidence to regular arrays of nonchiral subwavelength metamolecules in the form of strong circular dichroism and birefringence indistinguishable from those of chiral three-dimensional media
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