450 research outputs found
Theory of Low Temperature Electron Spin Resonance in Half-integer Spin Antiferromagnetic Chains
A theory of low temperature (T) electron spin resonance (ESR) in half-integer
spin antiferromagnetic chains is developed using field theory methods and
avoiding previous approximations. It is compared to experiments on Cu benzoate.
Power laws are predicted for the line-width broadening due to various types of
anisotropy. At T -> 0, zero width absorption peaks occur in some cases. The
second ESR peak in Cu benzoate, observed at T<.76K, is argued not to indicate
Neel order as previously claimed, but to correspond to a sine-Gordon "breather"
excitation.Comment: 4 pages, REVTEX, 3 PostScript figures embedded in tex
Dynamical Structure Factor in Cu Benzoate and other spin-1/2 antiferromagnetic chains
Recent experiments of the quasi-one-dimensional spin-1/2 antiferromagnet
Copper Benzoate established the existence of a magnetic field induced gap. The
observed neutron scattering intensity exhibits resolution limited peaks at both
the antiferromagnetic wave number and at incommensurate wave numbers related to
the applied magnetic field. We determine the ratio of spectral weights of these
peaks within the framework of a low-energy effective field theory description
of the problem.Comment: 5 pages, 3figure
Boundary Critical Phenomena in SU(3) "Spin" Chains
SU(3)-invariant "spin" chains with a single impurity, such as a modified
exchange coupling on one link, are analyzed using boundary conformal field
theory techniques. These chains are equivalent to a special case of the "tJV"
model, i.e. the t-J model with a nearest neighbour repulsion added. In the
continuum limit they are equivalent to two free bosons at a special value of
the compactification radii. The SU(3) symmetry, which is made explicit in this
formulation, provides insight into the exact solution of a non-trivial boundary
critical point found earlier in another formulation of this model as a theory
of quantum Brownian motion.Comment: 19 pages, Rev Te
Valence transition in the periodic Anderson model
A very rich phase diagram has recently been found in CeCuSi from
high pressure experiments where, in particular, a transition between an
intermediate valence configuration and an integral valent heavy fermion state
has been observed. We show that such a valence transition can be understood in
the framework of the periodic Anderson model. In particular, our results show a
breakdown of a mixed-valence state which is accompanied by a drastic change in
the \textit{f} occupation in agreement with experiment. This valence transition
can possibly be interpreted as a collapse of the large Fermi surface of the
heavy fermion state which incorporates not only the conduction electrons but
also the localized \textit{f} electrons. The theoretical approach used in this
paper is based on the novel projector-based renormalization method (PRM). With
respect to the periodic Anderson model, the method was before only employed in
combination with the basic approximations of the well-known slave-boson
mean-field theory. In this paper, the PRM treatment is performed in a more
sophisticated manner where both mixed as well as integral valent solutions have
been obtained. Furthermore, we argue that the presented PRM approach might be a
promising starting point to study the competing interactions in
CeCuSi and related compounds.Comment: 9 pages, 3 figures included; v2: completely revised and extended
versio
Maximized string order parameters in the valence bond solid states of quantum integer spin chains
We propose a set of maximized string order parameters to describe the hidden
topological order in the valence bond solid states of quantum integer spin-S
chains. These optimized string order parameters involve spin-twist angles
corresponding to rotations around or -axes, suggesting a
hidden symmetry. Our results also suggest that a local
triplet excitation in the valence bond solid states carries a
topological charge measured by these maximized string order parameters.Comment: 5 pages, 1 figur
Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains
The plateau-non-plateau transition in the
antiferromagnetic-(ferromagnetic) polymerized XXZ chains under
the magnetic field is investigated. The universality class of this transition
belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points
are determined by level spectroscopy analysis of the numerical diagonalization
data for where is the size of a unit cell.
It is found that the critical strength of ferromagnetic coupling decreases with
for small but increases for larger enough . It is also found that
the plateau for large is wide enough for moderate values of exchange
coupling so that it should be easily observed experimentally. This is in
contrast to the plateaus for chains which are narrow for a wide range
of exchange coupling even away from the critical point
Magnetization Plateau of an S=1 Frustrated Spin Ladder
We study the magnetization plateau at 1/4 of the saturation magnetization of
the S=1 antiferromagnetic spin ladder both analytically and numerically, with
the aim of explaining recent experimental results on BIP-TENO by Goto et al. We
propose two mechanisms for the plateau formation and clarify the plateau phase
diagram on the plane of the coupling constants between spins
ESR investigation on the Breather mode and the Spinon-Breather dynamical crossover in Cu Benzoate
A new elementary-excitation, the so called "breather excitation", is observed
directly by millimeter-submillimeter wave electron spin resonance (ESR) in the
Heisenberg quantum spin-chain Cu benzoate, in which a field-induced gap is
found recently by specific heat and neutron scattering measurements. Distinct
anomalies were found in line width and in resonance field around the "dynamical
crossover" regime between the gap-less spinon-regime and the gapped
breather-regime. When the temperature becomes sufficiently lower than the
energy gap, a new ESR-line with very narrow line-width is found, which is the
manifestation of the breather excitation. The non-linear field dependence of
the resonance field agrees well with the theoretical formula of the first
breather-excitation proposed by Oshikawa and Affleck. The present work
establishes experimentally for the first time that a sine-Gordon model is
applicable to explain spin dynamics in a S=1/2 Heisenberg spin chain subjected
to staggered field even in high fields.Comment: Revtex, 4 pages, 4 figures, submitted to Phys. Rev. Let
Mechanisms for Non-Trivial Magnetization Plateaux of an S=1 Frustrated Spin Ladder
We investigate the non-trivial magnetization plateau at 1/4 of the saturation
magnetization of S=1 spin ladder, especially with reference to recent
experimental results on a new organic tetraradical
3,3',5,5'-tetrakis(N-tert-butylaminoxyl)biphenyl, abbreviated as BIP-TENO. We
propose three mechanisms for the formation of the plateau; the Neel mechanism,
the dimer mechanism and the spin-Peierls mechanism. We also discuss the effect
of four-spin exchange interactions.Comment: 3 pages, 5 figures, Orbital2001 (International Conference on Strongly
Correlated Electrons with Orbital Degrees of Freedom) (September 11-14, 2001.
Sendai
Direct perturbation theory on the shift of Electron Spin Resonance
We formulate a direct and systematic perturbation theory on the shift of the
main paramagnetic peak in Electron Spin Resonance, and derive a general
expression up to second order. It is applied to one-dimensional XXZ and
transverse Ising models in the high field limit, to obtain explicit results
including the polarization dependence for arbitrary temperature.Comment: 5 pages (no figures) in REVTE
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