3,944 research outputs found
Spin wave calculation of the field-dependent magnetization pattern around an impurity in Heisenberg antiferromagnets
We consider the magnetic-field dependent spatial magnetization pattern around
a general impurity embedded in a Heisenberg antiferromagnet using both an
analytical and a numerical spin wave approach. The results are compared to
quantum Monte Carlo simulations. The decay of the magnetization pattern away
from the impurity follows a universal form which reflects the properties of the
pure antiferromagnetic Heisenberg model. Only the overall magnitude of the
induced magnetization depends also on the size of the impurity spin and the
impurity coupling.Comment: 11 pages, 11 figure
Wigner crystal vs. Friedel oscillations in the 1D Hubbard model
We analyze the fermion density of the one-dimensional Hubbard model using
bosonization and numerical DMRG calculations. For finite systems we find a
relatively sharp crossover even for moderate short range interactions into a
region with density waves as a function of density. The results show
that the unstable fixed point of a spin-incoherent state can dominate the
physical behavior in a large region of parameter space in finite systems. The
crossover may be observable in ultra cold fermionic gases in optical lattices
and in finite quantum wires.Comment: 6 pages, 6 figures. Published version. The most recent file can be
found at http://www.physik.uni-kl.de/eggert/papers/index.htm
Static impurities in a supersolid of interacting hard-core bosons on a triangular lattice
We study the effect of impurities in a supersolid phase in comparison to the
behavior in the solid and superfluid phases. A supersolid phase has been
established for interacting hardcore bosons on a triangular lattice which may
be realizable by ultracold atomic gases. Static vacancies are considered in
this model which always lower the magnitude of the order parameter in the solid
or superfluid phases. In the supersolid phase, however, the impurities directly
affect both order parameters simultaneously and thereby reveal an interesting
interplay between them. In particular the solid order may be enhanced at the
cost of a strong reduction of the superfluidity, which shows that the two order
parameters cannot be in a simple superposition. We also observe an unusual
impurity pinning effect in the solid ordered phase, which results in two
distinct states separated by a first-order transition.Comment: 5 pages, 5 figures, final version. More information at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Precision orbit computations for an operational environment
Taking advantage of the improvements to the Earth's gravitation field and tracking station coordinates, an orbital computational consistency of the order of 5 meters was achieved for total position differences between orbital solutions for the Seasat and GEOS-3. The main source of error in these solutions was in the mathematical models that are required to generate these results, i.e., gravitation, atmospheric drag, etc. Different Earth gravitation fields and tracking coordinates were analyzed and evaluated in obtaining these computational results. Comparisons and evaluations of the Seasat results were obtained in terms of different solution types such as the Doppler only, Laser only, Doppler and Laser, etc. Other investigation using the Seasat data were made in order to determine their effect on the computational results at this particular level of consistency
Universal alternating order around impurities in antiferromagnets
The study of impurities in antiferromagnets is of considerable interest in
condensed matter physics. In this paper we address the elementary question of
the effect of vacancies on the orientation of the surrounding magnetic moments
in an antiferromagnet. In the presence of a magnetic field, alternating
magnetic moments are induced, which can be described by a universal expression
that is valid in any ordered antiferromagnet and turns out to be independent of
temperature over a large range. The universality is not destroyed by quantum
fluctuation, which is demonstrated by quantum Monte Carlo simulations in the
two-dimensional Heisenberg antiferromagnet. Physical predictions for finite
doping are made, which are relevant for experiments probing Knight shifts and
the order parameter.Comment: 5 pages, 2 figures. The most recent version in PDF format can be
found at http://www.physik.uni-kl.de/eggert/papers
Trapping of dielectric particles with light-induced space-charge fields
Light-induced space-charge fields in lithium niobate crystals are used to trap and manipulate dielectric particles on the surface of such crystals. Without any external voltage source, strong field gradients are present in the proximity of the crystal surface. These are used to trap particles with diameters in the range between 100 nm and some tens of micrometers
Heritage Regimes and the State
What happens when UNESCO heritage conventions are ratified by a state? How do UNESCO’s global efforts interact with preexisting local, regional and state efforts to conserve or promote culture? What new institutions emerge to address the mandate? The contributors to this volume focus on the work of translation and interpretation that ensues once heritage conventions are ratified and implemented. With seventeen case studies from Europe, Africa, the Caribbean and China, the volume provides comparative evidence for the divergent heritage regimes generated in states that differ in history and political organization. The cases illustrate how UNESCO’s aspiration to honor and celebrate cultural diversity diversifies itself. The very effort to adopt a global heritage regime forces myriad adaptations to particular state and interstate modalities of building and managing heritage.What happens when UNESCO heritage conventions are ratified by a state? How do UNESCO’s global efforts interact with preexisting local, regional and state efforts to conserve or promote culture? What new institutions emerge to address the mandate? The contributors to this volume focus on the work of translation and interpretation that ensues once heritage conventions are ratified and implemented. With seventeen case studies from Europe, Africa, the Caribbean and China, the volume provides comparative evidence for the divergent heritage regimes generated in states that differ in history and political organization. The cases illustrate how UNESCO’s aspiration to honor and celebrate cultural diversity diversifies itself. The very effort to adopt a global heritage regime forces myriad adaptations to particular state and interstate modalities of building and managing heritage
Interaction effects between impurities in low dimensional spin-1/2 antiferromagnets
We are considering the interplay between several non-magnetic impurities in
the spin-1/2 Heisenberg antiferromagnet in chains, ladders and planes by
introducing static vacancies in numerical quantum Monte Carlo simulations. The
effective potential between two and more impurities is accurately determined,
which gives a direct measure of the quantum correlations in the systems. Large
effective interaction potentials are an indication of strong quantum
correlations in the system and reflect the detailed nature of the valence bond
ground states. In two-dimensions (2D) the interactions are smaller, but can
still be analyzed in terms of valence bonds.Comment: 8 pages, 6 figures, accepted by Europhys. Lett. The latest pdf file
is available at http://www.physik.uni-kl.de/eggert/papers/interact2d.pd
Heritage Regimes and the State
What happens when UNESCO heritage conventions are ratified by a state? How do UNESCO’s global efforts interact with preexisting local, regional and state efforts to conserve or promote culture? What new institutions emerge to address the mandate? The contributors to this volume focus on the work of translation and interpretation that ensues once heritage conventions are ratified and implemented. With seventeen case studies from Europe, Africa, the Caribbean and China, the volume provides comparative evidence for the divergent heritage regimes generated in states that differ in history and political organization. The cases illustrate how UNESCO’s aspiration to honor and celebrate cultural diversity diversifies itself. The very effort to adopt a global heritage regime forces myriad adaptations to particular state and interstate modalities of building and managing heritage
Highest weight state description of the isotropic spin-1 chain
We introduce an overcomplete highest weight state basis as a calculational
tool for the description of the isotropic spin-1 chain with bilinear exchange
coupling J1 and biquadratic coupling J2. The ground state can be expressed
exactly at the three special points in the phase diagram where the Hamiltonian
corresponds to a sum of nearest neighbor total spin projection operators
(J1=0>J2, J1=-J2<0, and J1=-J2/3<0). In particular, at the phase transition
point J1=-J2<0 it is possible to exactly compute the ground states, excited
states, expectation values, and correlation functions by using the new total
spin basis.Comment: 8 pages, 1 figure, the most recent version can be found at
http://www.physik.uni-kl.de/eggert/papers
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