2,138 research outputs found
Quantum planes and quantum cylinders from Poisson homogeneous spaces
Quantum planes and a new quantum cylinder are obtained as quantization of
Poisson homogeneous spaces of two different Poisson structures on classical
Euclidean group E(2).Comment: 13 pages, plain Tex, no figure
Polaronic transport induced by competing interfacial magnetic order in a LaCaMnO/BiFeO heterostructure
Using ultrafast optical spectroscopy, we show that polaronic behavior
associated with interfacial antiferromagnetic order is likely the origin of
tunable magnetotransport upon switching the ferroelectric polarity in a
LaCaMnO/BiFeO (LCMO/BFO) heterostructure. This is
revealed through the difference in dynamic spectral weight transfer between
LCMO and LCMO/BFO at low temperatures, which indicates that transport in
LCMO/BFO is polaronic in nature. This polaronic feature in LCMO/BFO decreases
in relatively high magnetic fields due to the increased spin alignment, while
no discernible change is found in the LCMO film at low temperatures. These
results thus shed new light on the intrinsic mechanisms governing
magnetoelectric coupling in this heterostructure, potentially offering a new
route to enhancing multiferroic functionality
Operator algebra quantum homogeneous spaces of universal gauge groups
In this paper, we quantize universal gauge groups such as SU(\infty), as well
as their homogeneous spaces, in the sigma-C*-algebra setting. More precisely,
we propose concise definitions of sigma-C*-quantum groups and sigma-C*-quantum
homogeneous spaces and explain these concepts here. At the same time, we put
these definitions in the mathematical context of countably compactly generated
spaces as well as C*-compact quantum groups and homogeneous spaces. We also
study the representable K-theory of these spaces and compute it for the quantum
homogeneous spaces associated to the universal gauge group SU(\infty).Comment: 14 pages. Merged with [arXiv:1011.1073
Ballistic Annihilation Kinetics: The Case of Discrete Velocity Distributions
The kinetics of the annihilation process, , with ballistic particle
motion is investigated when the distribution of particle velocities is {\it
discrete}. This discreteness is the source of many intriguing phenomena. In the
mean field limit, the densities of different velocity species decay in time
with different power law rates for many initial conditions. For a
one-dimensional symmetric system containing particles with velocity 0 and , there is a particular initial state for which the concentrations of all
three species as decay as . For the case of a fast ``impurity'' in a
symmetric background of and particles, the impurity survival
probability decays as . In a symmetric
4-velocity system in which there are particles with velocities and
, there again is a special initial condition where the two species
decay at the same rate, t^{-\a}, with \a\cong 0.72. Efficient algorithms
are introduced to perform the large-scale simulations necessary to observe
these unusual phenomena clearly.Comment: 18 text pages, macro file included, hardcopy of 9 figures available
by email request to S
Impurity Band Conduction in a High Temperature Ferromagnetic Semiconductor
The band structure of a prototypical dilute ferromagnetic semiconductor,
GaMnAs, is studied across the phase diagram via optical
spectroscopy. We prove that the Fermi energy () resides in a Mn induced
impurity band (IB). This conclusion is based upon careful analysis of the
frequency and temperature dependence of the optical conductivity
(). From our analysis of we infer
a large effective mass () of the carriers, supporting the view that
conduction occurs in an IB. Our results also provide useful insights into the
transport properties of Mn-doped GaAs.Comment: 4 pages, 4 figure
An Empirical Charge Transfer Potential with Correct Dissociation Limits
The empirical valence bond (EVB) method [J. Chem. Phys. 52, 1262 (1970)] has
always embodied charge transfer processes. The mechanism of that behavior is
examined here and recast for use as a new empirical potential energy surface
for large-scale simulations. A two-state model is explored. The main features
of the model are: (1) Explicit decomposition of the total system electron
density is invoked; (2) The charge is defined through the density decomposition
into constituent contributions; (3) The charge transfer behavior is controlled
through the resonance energy matrix elements which cannot be ignored; and (4) A
reference-state approach, similar in spirit to the EVB method, is used to
define the resonance state energy contributions in terms of "knowable"
quantities. With equal validity, the new potential energy can be expressed as a
nonthermal ensemble average with a nonlinear but analytical charge dependence
in the occupation number. Dissociation to neutral species for a gas-phase
process is preserved. A variant of constrained search density functional theory
is advocated as the preferred way to define an energy for a given charge.Comment: Submitted to J. Chem. Phys. 11/12/03. 14 pages, 8 figure
Flux through a hole from a shaken granular medium
We have measured the flux of grains from a hole in the bottom of a shaken
container of grains. We find that the peak velocity of the vibration, vmax,
controls the flux, i.e., the flux is nearly independent of the frequency and
acceleration amplitude for a given value of vmax. The flux decreases with
increasing peak velocity and then becomes almost constant for the largest
values of vmax. The data at low peak velocity can be quantitatively described
by a simple model, but the crossover to nearly constant flux at larger peak
velocity suggests a regime in which the granular density near the container
bottom is independent of the energy input to the system.Comment: 14 pages, 4 figures. to appear in Physical Review
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