1,111 research outputs found
Quantum phase transitions in a new exactly solvable quantum spin biaxial model with multiple spin interactions
The new integrable quantum spin model is proposed. The model has a biaxial
magnetic anisotropy of alternating coupling between spins together with
multiple spin interactions. Our model gives the possibility to exactly find
thermodynamic characteristics of the considered spin chain. The ground state of
the model can reveal spontaneous values of the total magnetic and
antiferromagnetic moments, caused by multiple spin couplings. Also, in the
ground state, depending on the strength of multiple spin couplings, our model
manifests several quantum critical points, some of which are governed by the
external magnetic field
Time-dependent spin-wave theory
We generalize the spin-wave expansion in powers of the inverse spin to
time-dependent quantum spin models describing rotating magnets or magnets in
time-dependent external fields. We show that in these cases, the spin operators
should be projected onto properly defined rotating reference frames before the
spin components are bosonized using the Holstein-Primakoff transformation. As a
first application of our approach, we calculate the reorganization of the
magnetic state due to Bose-Einstein condensation of magnons in the magnetic
insulator yttrium-iron garnet; we predict a characteristic dip in the
magnetization which should be measurable in experiments.Comment: 6 pages, 5 figures, final version published in PR
Integrable models of coupled Heisenberg chains
We show that the solutions of the Yang--Baxter equation invariant under the
action of the Yangian lead to inhomogenous vertex models. Starting
from a four dimensional representation of we obtain an integrable
family of coupled Heisenberg spin- chains. Some thermodynamical
properties of this model are studied by means of the algebraic Bethe Ansatz.Comment: 10 pages, latex, 5 postscript figure
Character of magnetic excitations in a quasi-one-dimensional antiferromagnet near the quantum critical points: Impact on magneto-acoustic properties
We report results of magneto-acoustic studies in the quantum spin-chain
magnet NiCl-4SC(NH) (DTN) having a field-induced ordered
antiferromagnetic (AF) phase. In the vicinity of the quantum critical points
(QCPs) the acoustic mode manifests a pronounced softening accompanied
by energy dissipation of the sound wave. The acoustic anomalies are traced up
to , where the thermodynamic properties are determined by fermionic
magnetic excitations, the "hallmark" of one-dimensional (1D) spin chains. On
the other hand, as established in earlier studies, the AF phase in DTN is
governed by bosonic magnetic excitations. Our results suggest the presence of a
crossover from a 1D fermionic to a 3D bosonic character of the magnetic
excitations in DTN in the vicinity of the QCPs.Comment: 5 pages, 4 figures. Accepted for publication by Phys. Rev
Commensurate-Incommensurate Phase Transitions for Multichain Quantum Spin Models: Exact Results
The behavior in an external magnetic field is studied for a wide class of
multichain quantum spin models. It is shown that the magnetic field together
with the interchain couplings cause commensurate-incommensurate phase
transitions between the gapless phases in the ground state. The conformal limit
of these models is studied and it is shown that the low-lying excitations for
the incommensurate phases are not independent. A scenario for the transition
from one to two space dimensions for the integrable multichain models is
proposed. The similarities in the external field behavior for the quantum
multichain spin models and a wide class of quantum field theories are
discussed. The exponents for the gaps caused by relevant perturbations of the
models are calculated.Comment: 23 pages, LaTeX, typos correcte
Non-specific cellular uptake of surface-functionalized quantum dots
We report a systematic empirical study of nanoparticle internalization into
cells via non-specific pathways. The nanoparticles were comprised of commercial
quantum dots (QDs) that were highly visible under a fluorescence confocal
microscope. Surface-modified QDs with basic biologically-significant moieties,
e.g. carboxyl, amino, streptavidin were used, in combination with the surface
derivatization with polyethylene glycol (PEG) in a range of immortalized cell
lines. Internalization rates were derived from image analysis and a detailed
discussion about the effect of nanoparticle size, charge and surface groups is
presented. We find that PEG-derivatization dramatically suppresses the
non-specific uptake while PEG-free carboxyl and amine functional groups promote
QD internalization. These uptake variations displayed a remarkable consistency
across different cell types. The reported results are important for experiments
concerned with cellular uptake of surface-functionalized nanomaterials, both
when non-specific internalization is undesirable and also when it is intended
for material to be internalized as efficiently as possible.
Published article at: http://iopscience.iop.org/0957-4484/21/28/285105/Comment: 14 pages 7 figure
Observation of the novel type of ordering: Spontaneous ferriquadrupolar order
Using Raman and infrared spectroscopies the spontaneous ferriquadrupolar
ordering has been observed in the rare-earth-based system KDy(MoO).
Ordered quadrupoles in the electron subsystem attend non-equivalent distortions
of rare-earth ions in the ordered phase. The mean field theory explaining the
onset of such a type of ordering has been constructed.Comment: 6 pages, 4 figure
Magnetic Excitations in the Spin-1 Anisotropic Heisenberg Antiferromagnetic Chain System NiCl-4SC(NH)
NiCl-4SC(NH) (DTN) is a quantum S=1 chain system with strong
easy-pane anisotropy and a new candidate for the Bose-Einstein condensation of
the spin degrees of freedom. ESR studies of magnetic excitations in DTN in
fields up to 25 T are presented. Based on analysis of the single-magnon
excitation mode in the high-field spin-polarized phase and previous
experimental results [Phys. Rev. Lett. 96, 077204 (2006)], a revised set of
spin-Hamiltonian parameters is obtained. Our results yield K,
K, and K for the anisotropy, intrachain, and interchain exchange
interactions, respectively. These values are used to calculate the
antiferromagnetic phase boundary, magnetization and the frequency-field
dependence of two-magnon bound-state excitations predicted by theory and
observed in DTN for the first time. Excellent quantitative agreement with
experimental data is obtained
Multichannel Kondo Screening in a One-Dimensional Correlated Electron System
We present the exact Bethe Ansatz solution of a multichannel model of one-
dimensional correlated electrons coupled antiferromagnetically to a magnetic
impurity of arbitrary spin S. The solution reveals that interactions in the
bulk make the magnetic impurity drive both spin and charge fluctuations,
producing a mixed valence at the impurity site, with an associated effective
spin S_eff > S in the presence of a magnetic field. The screening of the
impurity spin is controlled by its size independently of the number of
channels, in contrast to the multichannel Kondo effect for free electrons.Comment: 5 pages Revtex. Final revised version to appear in Europhys. Let
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