1,154 research outputs found
Excitation hierarchy of the quantum sine-Gordon spin chain in strong magnetic field
The magnetic excitation spectrum of copper pyrimidine dinitrate, a material
containing S=1/2 antiferromagnetic chains with alternating g-tensor and the
Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is
probed using submillimeter wave electron spin resonance spectroscopy. Ten
excitation modes are resolved in the low-temperature spectrum, and their
frequency-field diagram is systematically studied in magnetic fields up to 25
T. The experimental data are sufficiently detailed to make a very accurate
comparison with predictions based on the quantum sine-Gordon field theory.
Signatures of three breather branches and a soliton, as well as those of
several multi-particle excitation modes are identified.Comment: 4 RevTeX pages, 3 figure
Magnetic ordering of weakly coupled frustrated quantum spin chains
The ordering temperature of a quasi-one-dimensional system, consisting of
weakly interacting quantum spin-1/2 chains with antiferromagnetic
spin-frustrating couplings (or zig-zag ladder) is calculated. The results show
that a quantum critical point between two phases of the one-dimensional
subsystem plays a crucial role. If the one-dimensional subsystem is in the
antiferromagnetic-like phase in the ground state, similar to the phase of a
spin chain without frustration, weak couplings yield magnetic ordering of the
Neel type. For intra-chain spin-frustrating interactions larger than the
critical one (at which the quantum phase transition takes place), the
quasi-one-dimensional spin system manifests a spiral magnetic incommensurate
ordering. The obtained results of our quantum theory are compared with the
quasi-classical approximations. The calculated features of magnetic ordering
are expected to be generic for weakly coupled quantum spin chains with gapless
excitations and spin-frustrating nearest and next-nearest neighbor
interactions.Comment: 6 pages, 2 figure
Spin Dynamics in Chains with Next-Nearest-Neighbor Exchange Interactions
Low-energy magnetic excitations in the spin-1/2 chain compound
(CHN)CuCl [known as (6MAP)CuCl] are probed by means of
tunable-frequency electron spin resonance. Two modes with asymmetric (with
respect to the line) frequency-field dependences are resolved,
illuminating the striking incompatibility with a simple uniform
Heisenberg chain model. The unusual ESR spectrum is explained in terms of the
recently developed theory for spin-1/2 chains, suggesting the important role of
next-nearest-neighbor interactions in this compound. Our conclusion is
supported by model calculations for the magnetic susceptibility of
(6MAP)CuCl, revealing a good qualitative agreement with experiment
Magnetic excitations in the spin-1 anisotropic antiferromagnet
The spin-1 anisotropic antiferromagnet NiCl_2-4SC(NH2)_2 exhibits a
field-induced quantum phase transition that is formally analogous to
Bose-Einstein condensation. Here we present results of systematic high-field
electron spin resonance (ESR) experimental and theoretical studies of this
compound with a special emphasis on single-ion two-magnon bound states. In
order to clarify some remaining discrepancies between theory and experiment,
the frequency-field dependence of magnetic excitations in this material is
reanalyzed. In particular, a more comprehensive interpretation of the
experimental signature of single-ion two-magnon bound states is shown to be
fully consistent with theoretical results. We also clarify the structure of the
ESR spectrum in the so-called intermediate phase.Comment: 9 pages, 10 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
Electron Spin Resonance in sine-Gordon spin chains in the perturbative spinon regime
We report the low-temperature multi-frequency ESR studies of copper
pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating
-tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new
theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett.
82, 5136 (1999)]. Their theory, based on bosonization and the self-energy
formalism, can be applied for precise calculation of ESR parameters of
antiferromagnetic chains in the perturbative spinon regime. Excellent
quantitative agreement between the theoretical predictions and experiment is
obtained.Comment: 4 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
Electron Spin Resonance in a Spin-1/2 Heisenberg Strong-rung Ladder
Cu(CHN)Cl, a strong-rung spin-1/2 Heisenberg ladder compound,
is probed by means of electron spin resonance (ESR) spectroscopy in the
field-induced gapless phase above . The temperature dependence of the
ESR linewidth is analyzed in the quantum field theory framework, suggesting
that the anisotropy of magnetic interactions plays a crucial role, determining
the peculiar low-temperature ESR linewidth behavior. In particular, it is
argued that the uniform Dzyaloshinskii-Moriya interaction (which is allowed on
the bonds along the ladder legs) can be the source of this behavior in
Cu(CHN)Cl
Dynamics of a Heisenberg spin chain in the quantum critical regime: NMR experiment versus effective field theory
A comprehensive comparison between the magnetic field- and
temperature-dependent low frequency spin dynamics in the antiferromagnetic
spin-1/2 Heisenberg chain (AFHC) system copper pyrazine dinitrate, probed via
the 13C-nuclear magnetic resonance (NMR) relaxation rate 1/T1, and the field
theoretical approach in the Luttinger liquid (LL) regime has been performed. We
have found a very good agreement between the experiment and theory in the
investigated temperature and field range. Our results demonstrate how strongly
the quantum critical point affects the spin dynamics of Heisenberg spin chain
compounds.Comment: 5 pages, 3 figure
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
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