55,628 research outputs found
Thermodynamical Bethe Ansatz and Condensed Matter
The basics of the thermodynamic Bethe ansatz equation are given. The simplest
case is repulsive delta function bosons, the thermodynamic equation contains
only one unknown function. We also treat the XXX model with spin 1/2 and the
XXZ model and the XYZ model. This method is very useful for the investigation
of the low temperature thermodynamics of solvable systems.Comment: 52 pages, 6 figures, latex, lamuphys.st
Entanglement Scaling in the One-Dimensional Hubbard Model at Criticality
We derive exact expressions for the local entanglement entropy E in the
ground state of the one-dimensional Hubbard model at a quantum phase transition
driven by a change in magnetic field h or chemical potential u. The leading
divergences of dE/dh and dE/du are shown to be directly related to those of the
zero-temperature spin and charge susceptibilities. Logarithmic corrections to
scaling signal a change in the number of local states accessible to the system
as it undergoes the transition.Comment: 4+ pages, 2 figures. Fig. 2 and minor typos correcte
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
Ground-state factorization and quantum phase transition in dimerized spin chains
We study the occurrence of ground-state factorization in dimerized spin
chains in a transverse field. Together with the usual ferromagnetic and
antiferromagnetic regimes, a third case emerges, with no analogous in
translationally-invariant systems, consisting of an antiferromagnetic
Ne\'{e}l-type ground state where pairs of spins represent the unitary cell.
Then, we calculate the exact solution of the model and show that the
factorizing field represent an accidental degeneracy point of the Hamiltonian.
Finally, we extend the study of the existence of ground-state factorization to
a more general class of models
Spin Squeezing via One-Axis Twisting with Coherent Light
We propose a new method of spin squeezing of atomic spin, based on the
interactions between atoms and off-resonant light which are known as
paramagnetic Faraday rotation and fictitious magnetic field of light. Since the
projection process, squeezed light, or special interactions among the atoms are
not required in this method, it can be widely applied to many systems. The
attainable range of the squeezing parameter is S^{-2/5}, where S is the total
spin, which is limited by additional fluctuations imposed by coherent light and
the spherical nature of the spin distribution.Comment: 4 pages,6 figure
Modified Spin Wave Analysis of Low Temperature Properties of Spin-1/2 Frustrated Ferromagnetic Ladder
Low temperature properties of the spin-1/2 frustrated ladder with
ferromagnetic rungs and legs, and two different antiferromagnetic next nearest
neighbor interaction are investigated using the modified spin wave
approximation in the region with ferromagnetic ground state. The temperature
dependence of the magnetic susceptibility and magnetic structure factors is
calculated. The results are consistent with the numerical exact diagonalization
results in the intermediate temperature range. Below this temperature range,
the finite size effect is significant in the numerical diagonalization results,
while the modified spin wave approximation gives more reliable results. The low
temperature properties near the limit of the stability of the ferromagnetic
ground state are also discussed.Comment: 9 pages, 8 figure
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