77 research outputs found
Color Screening, Casimir Scaling, and Domain Structure in G(2) and SU(N) Gauge Theories
We argue that screening of higher-representation color charges by gluons
implies a domain structure in the vacuum state of non-abelian gauge theories,
with the color magnetic flux in each domain quantized in units corresponding to
the gauge group center. Casimir scaling of string tensions at intermediate
distances results from random spatial variations in the color magnetic flux
within each domain. The exceptional G(2) gauge group is an example rather than
an exception to this picture, although for G(2) there is only one type of
vacuum domain, corresponding to the single element of the gauge group center.
We present some numerical results for G(2) intermediate string tensions and
Polyakov lines, as well as results for certain gauge-dependent projected
quantities. In this context, we discuss critically the idea of projecting link
variables to a subgroup of the gauge group. It is argued that such projections
are useful only when the representation-dependence of the string tension, at
some distance scale, is given by the representation of the subgroup.Comment: 24 pages, 14 figures; v2: references added; v3: published version
containing some additional introductory discussio
Center Vortices and the Gribov Horizon
We show how the infinite color-Coulomb energy of color-charged states is
related to enhanced density of near-zero modes of the Faddeev-Popov operator,
and calculate this density numerically for both pure Yang-Mills and gauge-Higgs
systems at zero temperature, and for pure gauge theory in the deconfined phase.
We find that the enhancement of the eigenvalue density is tied to the presence
of percolating center vortex configurations, and that this property disappears
when center vortices are either removed from the lattice configurations, or
cease to percolate. We further demonstrate that thin center vortices have a
special geometrical status in gauge-field configuration space: Thin vortices
are located at conical or wedge singularities on the Gribov horizon. We show
that the Gribov region is itself a convex manifold in lattice configuration
space. The Coulomb gauge condition also has a special status; it is shown to be
an attractive fixed point of a more general gauge condition, interpolating
between the Coulomb and Landau gauges.Comment: 19 pages, 17 EPS figures, RevTeX4; v2: added references, corrected
caption of fig. 11; v3: new data for higher couplings, clarifications on
color-Coulomb potential in deconfined phase, version to appear in JHE
Fast optical control of spin in semiconductor interfacial structures
We report on a picosecond-fast optical removal of spin polarization from a
self-confined photo-carrier system at an undoped GaAs/AlGaAs interface
possessing superior long-range and high-speed spin transport properties. We
employed a modified resonant spin amplification technique with unequal
intensities of subsequent pump pulses to experimentally distinguish the
evolution of spin populations originating from different excitation laser
pulses. We demonstrate that the density of spins, which is injected into the
system by means of the optical orientation, can be controlled by reducing the
electrostatic confinement of the system using an additional generation of
photocarriers. It is also shown that the disturbed confinement recovers within
hundreds of picoseconds after which spins can be again photo-injected into the
system
Tunneling anisotropic magnetoresistance in multilayer-(Co/Pt)/AlOx/Pt structures
We report observations of tunneling anisotropic magnetoresitance (TAMR) in
vertical tunnel devices with a ferromagnetic multilayer-(Co/Pt) electrode and a
non-magnetic Pt counter-electrode separated by an AlOx barrier. In stacks with
the ferromagnetic electrode terminated by a Co film the TAMR magnitude
saturates at 0.15% beyond which it shows only weak dependence on the magnetic
field strength, bias voltage, and temperature. For ferromagnetic electrodes
terminated by two monolayers of Pt we observe order(s) of magnitude enhancement
of the TAMR and a strong dependence on field, temperature and bias. Discussion
of experiments is based on relativistic ab initio calculations of magnetization
orientation dependent densities of states of Co and Co/Pt model systems.Comment: 4 pages, 5 figures, to be published in Phys. Rev. Let
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Noise-based approximation to thermal spin-injection in Fe/GaAs
© 2017 Author(s). We analyze the prospects for thermal spin-injection from iron into gallium arsenide via the application of electrical noise. By estimating the applied effective temperature-equivalent gradients, we characterize the magnitude of any electrical part of the thermal spin-injection efficiency or the spin-dependent Seebeck effect. The magnitude of the non-local spin signal associated with this effect suggests that temperature differences on the order of ∼100 K would be needed for true thermal spin-injection experiments. The large size of the effective temperature gradients induced by the noise-based method means that even very small thermo-electric effects can be quantified
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