38,394 research outputs found
Pre-K-Edge Structure on Anomalous X-Ray Scattering in LaMnO3
We study the pre-K-edge structure of the resonant X-ray scattering for
forbidden reflections (anomalous scattering) in LaMnO3, using the band
calculation based on the local density approximation. We find a two-peak
structure with an intensity approximately 1/100 of that of the main peak. This
originates from a mixing of 4p states of Mn to 3d states of neighboring Mn
sites. The effect is enhanced by an interference with the tail of the main
peak. The effect of the quadrupole transition is found to be one order of
magnitude smaller than that of the dipole transition, modifying slightly the
azimuthal-angle dependence.Comment: 4 pages, 5 figures, submitted to J. Phys. Soc. Jp
Renormalization-Group Approach to Spin-Wave Theory of Quantum Heisenberg Ferromagnet
The renormalization-group method is used to analyze the low-temperature
behaviour of a two-dimentional, spin- quantum Heisenberg ferromagnet. A set
of recursion equations is derived in an one-loop approximation. The
low-temperature asymptotics of the correlation length and the uniform
susceptibility are obtained. For small spins () the results are
essentially different from those in the spin-wave theory.Comment: 9 pages, RevTex 3.0 fil
Magnetic susceptibility and low-temperature specific-heat of integrable 1-D Hubbard model under open-boundary conditions
The magnetic susceptibility and the low-temperature specific heat of the
1-dimensional Hubbard model under the integrable open-boundary conditions are
discussed through the Bethe ansatz with the string hypothesis. The
contributions of the boundary fields to both the susceptibility and the
specific heat are obtained, and their exact expressions are analytically
derived.Comment: 14 pages, Latex, No figures, to appear in J. Phys. A: Gen. & Mat
One-dimensional superfluid Bose-Fermi mixture: mixing, demixing and bright solitons
We study a ultra-cold and dilute superfluid Bose-Fermi mixture confined in a
strictly one-dimensional atomic waveguide by using a set of coupled nonlinear
mean-field equations obtained from the Lieb-Liniger energy density for bosons
and the Gaudin-Yang energy density for fermions. We consider a finite
Bose-Fermi inter-atomic strength g_{bf} and both periodic and open boundary
conditions. We find that with periodic boundary conditions, i.e. in a quasi-1D
ring, a uniform Bose-Fermi mixture is stable only with a large fermionic
density. We predict that at small fermionic densities the ground state of the
system displays demixing if g_{bf}>0 and may become a localized Bose-Fermi
bright soliton for g_{bf}<0. Finally, we show, using variational and numerical
solution of the mean-field equations, that with open boundary conditions, i.e.
in a quasi-1D cylinder, the Bose-Fermi bright soliton is the unique ground
state of the system with a finite number of particles, which could exhibit a
partial mixing-demixing transition. In this case the bright solitons are
demonstrated to be dynamically stable. The experimental realization of these
Bose-Fermi bright solitons seems possible with present setups.Comment: 11 pages, 11 figure
Order-disorder transition in nanoscopic semiconductor quantum rings
Using the path integral Monte Carlo technique we show that semiconductor
quantum rings with up to six electrons exhibit a temperature, ring diameter,
and particle number dependent transition between spin ordered and disordered
Wigner crystals. Due to the small number of particles the transition extends
over a broad temperature range and is clearly identifiable from the electron
pair correlation functions.Comment: 4 pages, 5 figures, For recent information on physics of small
systems see http://www.smallsystems.d
Quantum Spin Chains and Riemann Zeta Function with Odd Arguments
Riemann zeta function is an important object of number theory. It was also
used for description of disordered systems in statistical mechanics. We show
that Riemann zeta function is also useful for the description of integrable
model. We study XXX Heisenberg spin 1/2 anti-ferromagnet. We evaluate a
probability of formation of a ferromagnetic string in the anti-ferromagnetic
ground state in thermodynamics limit. We prove that for short strings the
probability can be expressed in terms of Riemann zeta function with odd
arguments.Comment: LaTeX, 7 page
TFD Approach to Bosonic Strings and -branes
In this work we explain the construction of the thermal vacuum for the
bosonic string, as well that of the thermal boundary state interpreted as a
-brane at finite temperature. In both case we calculate the respective
entropy using the entropy operator of the Thermo Field Dynamics Theory. We show
that the contribution of the thermal string entropy is explicitly present in
the -brane entropy. Furthermore, we show that the Thermo Field approach
is suitable to introduce temperature in boundary states.Comment: 6 pages, revtex, typos are corrected. Prepared for the Second
Londrina Winter School-Mathematical Methods in Physics, August 25-30, 2002,
Londrina-Pr, Brazil. To appear in a special issue of IJMP
Dynamics of a single exciton in strongly correlated bilayers
We formulated an effective theory for a single interlayer exciton in a
bilayer quantum antiferromagnet, in the limit that the holon and doublon are
strongly bound onto one interlayer rung by the Coulomb force. Upon using a rung
linear spin wave approximation of the bilayer Heisenberg model, we calculated
the spectral function of the exciton for a wide range of the interlayer
Heisenberg coupling \alpha=J_{\perp}/Jz. In the disordered phase at large
\alpha, a coherent quasiparticle peak appears representing free motion of the
exciton in a spin singlet background. In the N\'{e}el phase, which applies to
more realistic model parameters, a ladder spectrum arises due to Ising
confinement of the exciton. The exciton spectrum is visible in measurements of
the dielectric function, such as c-axis optical conductivity measurements.Comment: 28 pages, 12 figure
Non-regular eigenstate of the XXX model as some limit of the Bethe state
For the one-dimensional XXX model under the periodic boundary conditions, we
discuss two types of eigenvectors, regular eigenvectors which have
finite-valued rapidities satisfying the Bethe ansatz equations, and non-regular
eigenvectors which are descendants of some regular eigenvectors under the
action of the SU(2) spin-lowering operator. It was pointed out by many authors
that the non-regular eigenvectors should correspond to the Bethe ansatz
wavefunctions which have multiple infinite rapidities. However, it has not been
explicitly shown whether such a delicate limiting procedure should be possible.
In this paper, we discuss it explicitly in the level of wavefunctions: we prove
that any non-regular eigenvector of the XXX model is derived from the Bethe
ansatz wavefunctions through some limit of infinite rapidities. We formulate
the regularization also in terms of the algebraic Bethe ansatz method. As an
application of infinite rapidity, we discuss the period of the spectral flow
under the twisted periodic boundary conditions.Comment: 53 pages, no figur
Critical properties and R\'enyi entropies of the spin-3/2 XXZ chain
We discuss entanglement and critical properties of the spin-3/2 XXZ chain in
its entire gapless region. Employing density-matrix renormalization group
calculations combined with different methods based on level spectroscopy,
correlation functions and entanglement entropies, we determine the sound
velocity and the Luttinger parameter of the model as a function of the
anisotropy parameter. Then, we focus on entanglement properties by
systematically studying the behavior of R\'enyi entropies under both open and
periodic boundary conditions, providing further evidence of recent findings
about entanglement entropies of excited states in conformal field theory.Comment: 8 pages, 10 figures; small text revisions and a new figure. Accepted
for publication in Phys. Rev.
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