837 research outputs found
Heat Transport in Spin Chains with Weak Spin-Phonon Coupling
The heat transport in a system of large- Heisenberg spin chains,
describing closely SrCuO and SrCuO cuprates, is studied
theoretically at by considering interactions of the bosonized spin
excitations with optical phonons and defects. Treating rigorously the
multi-boson processes, we derive a microscopic spin-phonon scattering rate that
adheres to an intuitive picture of phonons acting as thermally populated
defects for the fast spin excitations. The mean-free path of the latter
exhibits a distinctive -dependence reflecting a critical nature of spin
chains and gives a close description of experiments. By the naturalness
criterion of realistically small spin-phonon interaction, our approach stands
out from previous considerations that require large coupling constants to
explain the data and thus imply a spin-Peierls transition, absent in real
materials.Comment: 5+ pages main text, 4+ pages supplemental, 4+2 figures, adiabatic
approximation to the published versio
The representations of the Hubbard algebra in terms of spin-fermion operators and motion of a hole in an antiferromagnetic state
The representation of the Hubbard operators in terms of the
spin operators and the fermion operator with spin
is proposed.
In the low-energy limit this representation is reduced to the representation
following from the Hubbard diagramm technique. In framework of this approach
motion of a hole in an antiferromagnetic state of the t-J model is considered.
It is shown that the primary hole energy is strongly renormalized and the band
width has an order of J rather than t.
The functional integral for the strongly correlated model induced by the
obtained representation is formulated. The representation of the total Hubbard
algebra for states in the lower and the upper Hubbard bands is formulated in
terms of the spin and two fermion fields with spin
is formulated.Comment: 12 pp. (LATEX
N 3-[(E)-Morpholin-4-ylÂmethylÂidene]-1-phenyl-1H-1,2,4-triazole-3,5-diamine monohydrate
In the title compound, C13H16N6O·H2O, the mean planes of the benzene and 1,2,4-triazole rings form a dihedral angle of 54.80 (5)°. The N atom of the amino group adopts a trigonal–pyramidal configuration. Conjugation in the amidine N=C—N fragment results in sufficient shortening of the formal single bond. In the crystal, interÂmolecular N—H⋯O and O—H⋯N hydrogen bonds link molÂecules into double layers parallel to the bc plane
Spinon-holon interactions in an anisotropic t-J chain: a comprehensive study
We consider a generalization of the one-dimensional t-J model with
anisotropic spin-spin interactions. We show that the anisotropy leads to an
effective attractive interaction between the spinon and holon excitations,
resulting in a localized bound state. Detailed quantitative analytic
predictions for the dependence of the binding energy on the anisotropy are
presented, and verified by precise numerical simulations. The binding energy is
found to interpolate smoothly between a finite value in the t-Jz limit and zero
in the isotropic limit, going to zero exponentially in the vicinity of the
latter. We identify changes in spinon dispersion as the primary factor for this
non-trivial behavior.Comment: 12 pages, 13 figures, long story. The short story is
cond-mat/0702213. Published versio
Binding of holons and spinons in the one-dimensional anisotropic t-J model
We study the binding of a holon and a spinon in the one-dimensional
anisotropic t-J model using a Bethe-Salpeter equation approach, exact
diagonalization, and density matrix renormalization group methods on chains of
up to 128 sites. We find that holon-spinon binding changes dramatically as a
function of anisotropy parameter \alpha=J_\perp/J_z: it evolves from an exactly
deducible impurity-like result in the Ising limit to an exponentially shallow
bound state near the isotropic case. A remarkable agreement between the theory
and numerical results suggests that such a change is controlled by the
corresponding evolution of the spinon energy spectrum.Comment: 4 pages, 5 figures, published versio
Acoustic instability of a circular vortex with a smoothed vorticity profile
It is known that a localized vortex can have two specific mechanisms of
interaction with the ambient flow. The first mechanism is associated with
acoustic radiation, which is accompanied by a loss of energy and causes
instability in the case of negative energy of vortex disturbances. The second
is a Miles mechanism of interaction of the vortex core oscillations with
disturbances in the vicinity of the critical layer (where the phase velocity of
the disturbances coincides with the velocity of the mean flow), accompanied by
an energy flux from the critical layer vicinity, which leads to damping in the
case of negative energy of the oscillations. For the first time, the flow with
both of these mechanisms is considered. The problem is solved from the first
principles. It is shown that the Miles mechanism can completely suppress
acoustic instability, however, in the case of a stronger loss of energy due to
acoustic radiation, acoustic instability will dominate. The role of various
parameters is analyzed and a quantitative criterion for the acoustic
instability of a vortex with a smoothed vorticity profile is obtained
Crystal structure of mixed fluorites Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) and luminescence of Eu(2+) in the crystals
Within the framework of the virtual crystal method implemented in the shell
model and pair potential approximation the crystal structure of mixed fluorites
Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) has been calculated. The impurity center
Eu(2+) and the distance Eu(2+)-F in this crystals have been also calculated.
The low level position of excited 4f65d configuration of the Eu(2+) ion has
been expressed using phenomenological dependence on distance E(2+)-F. The
dependences of Stokes shift and Huang-Rhys factor on concentration x have been
received for yellow luminescence in Sr(1-x)Ba(x)F(2):Eu(2+). The value x, for
which the eg -level of Eu(2+) ion will be in conduction band in
Sr(1-x)Ba(x)F(2):Eu(2+) has been calculated.Comment: 8 pages, 3 figures. The manuscript is sent to journal 'Physics of the
solid state'. The results will be submitted on inernational conference
SCINTMAT'2002 in oral session (june,20-22,2002,Ekaterinburg,Russia).
Corresponding author e-mail: [email protected]
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