2,883 research outputs found
Itinerant Ferromagnetism in ultracold Fermi gases
Itinerant ferromagnetism in cold Fermi gases with repulsive interactions is
studied applying the Jastrow-Slater approximation generalized to finite
polarization and temperature. For two components at zero temperature a second
order transition is found at compatible with QMC.
Thermodynamic functions and observables such as the compressibility and spin
susceptibility and the resulting fluctuations in number and spin are
calculated. For trapped gases the resulting cloud radii and kinetic energies
are calculated and compared to recent experiments. Spin polarized systems are
recommended for effective separation of large ferromagnetic domains. Collective
modes are predicted and tri-critical points are calculated for multi-component
systems.Comment: 8 pages, 6 figure
Correlated versus Ferromagnetic State in Repulsively Interacting Two-Component Fermi Gases
Whether a spin-1/2 Fermi gas will become ferromagnetic as the strength of
repulsive interaction increases is a long-standing controversial issue.
Recently this problem is studied experimentally by Jo et al, Science, 325, 1521
(2009) in which the authors claim a ferromagnetic transition is observed. This
work is to point out the results of this experiment can not distinguish whether
the system is in a ferromagnetic state or in a non-magnetic but strongly
short-range correlated state. A conclusive experimental demonstration of
ferromagnetism relies on the observation of ferromagnetic domains.Comment: 4 pages, 2 figures, published versio
Quantum Hall Ferromagnetism in Graphene
Graphene is a two-dimensional carbon material with a honeycomb lattice and
Dirac-like low-energy excitations. When Zeeman and spin-orbit interactions are
neglected its Landau levels are four-fold degenerate, explaining the
separation between quantized Hall conductivity values seen in recent
experiments. In this paper we derive a criterion for the occurrence of
interaction-driven quantum Hall effects near intermediate integer values of
due to charge gaps in broken symmetry states.Comment: 4 pages, 1 figur
Physiochemical, site, and bidirectional reflectance factor characteristics of uniformly moist soils
The author has identified the following significant results. The bidirectional reflectance factor (0.5 micron to 2.3 micron wavelength interval) and physiochemical properties of over 500 soils from 39 states, Brazil and Spain were measured. Site characteristics of soil temperature regime and moisture zone were used as selection criteria. Parent material and internal drainage were noted for each soil. At least five general types of soil reflectance curves were identified based primarily on the presence or absence of ferric iron absorption bands, organic matter content, and soil drainage characteristics. Reflectance in 10 bands across the spectrum was found to be negatively correlated with the natural log of organic matter content
Characteristic variations in reflectance of surface soils
Surface soil samples from a wide range of naturally occurring soils were obtained for the purpose of studying the characteristic variations in soil reflectance as these variations relate to other soil properties and soil classification. A total 485 soil samples from the U.S. and Brazil representing 30 suborders of the 10 orders of 'Soil Taxonomy' was examined. The spectral bidirectional reflectance factor was measured on uniformly moist soils over the 0.52 to 2.32 micron wavelength range with a spectroradiometer adapted for indoor use. Five distinct soil spectral reflectance curve forms were identified according to curve shape, the presence or absence of absorption bands, and the predominance of soil organic matter and iron oxide composition. These curve forms were further characterized according to generically homogeneous soil properties in a manner similar to the subdivisions at the suborder level of 'Soil Taxonomy'. Results indicate that spectroradiometric measurements of soil spectral bidirectional reflectance factor can be used to characterize soil reflectance in terms that are meaningful to soil classification, genesis, and survey
Environment assisted degradation mechanisms in advanced light metals
The general goals of the research program are to characterize alloy behavior quantitatively and to develop predictive mechanisms for environmental failure modes. Successes in this regard will provide the basis for metallurgical optimization of alloy performance, for chemical control of aggressive environments, and for engineering life prediction with damage tolerance and long term reliability
Itinerant ferromagnetism in the multiorbital Hubbard model: a dynamical mean-field study
In order to resolve the long-standing issue of how the itinerant
ferromagnetism is affected by the lattice structure and Hund's coupling, we
have compared various three-dimensional lattice structures in the single- and
multiorbital Hubbard models with the dynamical mean-field theory with an
improved quantum Monte Carlo algorithm that preserves the spin-SU(2) symmetry.
The result indicates that {\it both} the lattice structure and the d-orbital
degeneracy are essential for the ferromagnetism in the parameter region
representing a transition metal. Specifically, (a) Hund's coupling, despite the
common belief, is important, which is here identified to come from
particle-hole scatterings, and (b) the ferromagnetism is a correlation effect
(outside the Stoner picture) as indicated from the band-filling dependence.Comment: 4 pages, 5 figure
Stability of a Fully Magnetized Ferromagnetic state in Repulsively Interacting Ultracold Fermi Gases
We construct a variational wave function to study whether a fully polarized
Fermi sea is energetically stable against a single spin flip. Our variational
wave function contains sufficient short-range correlation at least to the same
level as Gutzwiller's projected wave function. For Hubbard lattice model and
continuum model with pure repulsive interaction, we show a fully polarized
Fermi sea is generally unstable even when the repulsive strength becomes
infinite. While for a resonance model, ferromagnetic state is possible if the
s-wave scattering length is positive and sufficiently large, and the system is
prepared in scattering state orthogonal to molecular bound state. However, we
can not rule out the possibility that more exotic correlation can destabilize
the ferromagnetic state.Comment: 4 pages, 3 figure
Determining density of maize canopy. 2: Airborne multispectral scanner data
Multispectral scanner data were collected in two flights over a light colored soil background cover plot at an altitude of 305 m. Energy in eleven reflective wavelength band from 0.45 to 2.6 microns was recorded. Four growth stages of maize (Zea mays L.) gave a wide range of canopy densities for each flight date. Leaf area index measurements were taken from the twelve subplots and were used as a measure of canopy density. Ratio techniques were used to relate uncalibrated scanner response to leaf area index. The ratios of scanner data values for the 0.72 to 0.92 micron wavelength band over the 0.61 to 0.70 micron wavelength band were calculated for each plot. The ratios related very well to leaf area index for a given flight date. The results indicated that spectral data from maize canopies could be of value in determining canopy density
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