9,256 research outputs found
Density matrix for the kink ground state of the ferromagnetic XXZ chain
The exact expression for the density matrix of the kink ground state of the
ferromagnetic XXZ chain is obtained. Utilizing this, we exactly calculate
various correlation functions such as the longitudinal and transverse spin-spin
correlation functions, and the ferromagnetic and antiferromagnetic string
formation probabilities. The asymptotic behaviors of these correlation
functions are also analyzed. As a consequence, we find that the spin-spin
correlation functions decay exponentially for large distances, while the string
formation probabilities exhibit Gaussian decay for large strings. We also
evaluate the entanglement entropy, which shows interesting behaviors due to the
lack of the translational invariance of the state.Comment: 7 pages, 9 figure
Free energies and critical exponents of the A_1^{(1)}, B_n^{(1)}, C_n^{(1)} and D_n^{(1)} face models
We obtain the free energies and critical exponents of models associated with
elliptic solutions of the star-triangle relation and reflection equation. The
models considered are related to the affine Lie algebras A_1^{(1)},
B_n^{(1)},C_n^{(1)} and D_n^{(1)}. The bulk and surface specific heat exponents
are seen to satisfy the scaling relation 2\alpha_s = \alpha_b + 2. It follows
from scaling relations that in regime III the correlation length exponent \nu
is given by \nu=(l+g)/2g, where l is the level and g is the dual Coxeter
number. In regime II we find \nu=(l+g)/2l.Comment: 9 pages, Latex, no figure
Quantum spin chains in a magnetic field
We demonstrate that the ``worm'' algorithm allows very effective and precise
quantum Monte Carlo (QMC) simulations of spin systems in a magnetic field, and
its auto-correlation time is rather insensitive to the value of H at low
temperature. Magnetization curves for the and chains are
presented and compared with existing Bethe ansatz and exact diagonalization
results. From the Green function analysis we deduce the magnon spectra in the
s=1 system, and directly establish the "relativistic" form E(p)=(\Delta ^2 +v^2
p^2)^{1/2} of the dispersion law.Comment: 6 pages, 8 figures; removed discussion of spin-2 case - will be
published later in a separate pape
Transport Coefficients of the Anderson Model via the Numerical Renormalization Group
The transport coefficients of the Anderson model are calculated by extending
Wilson's NRG method to finite temperature Green's functions. Accurate results
for the frequency and temperature dependence of the single--particle spectral
densities and transport time are obtained and used to extract
the temperature dependence of the transport coefficients in the strong
correlation limit. The low temperature anomalies in the resistivity, ,
thermopower, , thermal conductivity and Hall coefficient,
, are discussed. All quantities exhibit the expected Fermi liquid
behaviour at low temperature with power law dependecies on in very
good agreement with analytic results based on Fermi liquid theory. Scattering
of conduction electrons in higher, , angular momentum channels is also
considered and an expression is derived for the corresponding transport time
and used to discuss the influence of non--resonant scattering on the transport
properties.Comment: 45 pages, RevTeX, 28 figures, available on reques
An Electron Spin Resonance Selection Rule for Spin-Gapped Systems
The direct electron spin resonance (ESR) absorption between a singlet ground
state and the triplet excited states of spin gap systems is investigated. Such
an absorption, which is forbidden by the conservation of the total spin quantum
number in isotropic Hamiltonians, is allowed by the Dzyaloshinskii-Moriya
interaction. We show a selection rule in the presence of this interaction,
using the exact numerical diagonalization of the finite cluster of the
quasi-one-dimensional bond-alternating spin system. The selection rule is also
modified into a suitable form in order to interpret recent experimental results
on CuGeO and NaVO.Comment: 5 pages, Revtex, with 6 eps figures, to appear in J. Phys. Soc. Jpn.
Vol. 69 No. 11 (2000
Magnetothermal transport in the spin-1/2 chains of copper pyrazine dinitrate
We present experiments on the thermal transport in the spin-1/2 chain
compound copper pyrazine dinitrate Cu(C_4 H_4 N_2)(NO_3)_2. The heat
conductivity shows a surprisingly strong dependence on the applied magnetic
field B, characterized at low temperatures by two main features. The first one
appearing at low B is a characteristic dip located at mu_B B ~ k_B T, that may
arise from Umklapp scattering. The second one is a plateau-like feature in the
quantum critical regime, mu_B |B-B_c| < k_B T, where B_c is the saturation
field at T=0. The latter feature clearly points towards a momentum and field
independent mean free path of the spin excitations, contrary to theoretical
expectations.Comment: 4 pages, 4 figure
Conductance Distribution in Disordered Quantum Wires with a Perfectly Conducting Channel
We study the conductance of phase-coherent disordered quantum wires focusing
on the case in which the number of conducting channels is imbalanced between
two propagating directions. If the number of channels in one direction is by
one greater than that in the opposite direction, one perfectly conducting
channel without backscattering is stabilized regardless of wire length.
Consequently, the dimensionless conductance does not vanish but converges to
unity in the long-wire limit, indicating the absence of Anderson localization.
To observe the influence of a perfectly conducting channel, we numerically
obtain the distribution of conductance in both cases with and without a
perfectly conducting channel. We show that the characteristic form of the
distribution is notably modified in the presence of a perfectly conducting
channel.Comment: 7 pages, 16 figure
Non-Abelian Walls in Supersymmetric Gauge Theories
The Bogomol'nyi-Prasad-Sommerfield (BPS) multi-wall solutions are constructed
in supersymmetric U(N_C) gauge theories in five dimensions with N_F(>N_C)
hypermultiplets in the fundamental representation. Exact solutions are obtained
with full generic moduli for infinite gauge coupling and with partial moduli
for finite gauge coupling. The generic wall solutions require nontrivial
configurations for either gauge fields or off-diagonal components of adjoint
scalars depending on the gauge. Effective theories of moduli fields are
constructed as world-volume gauge theories. Nambu-Goldstone and
quasi-Nambu-Goldstone scalars are distinguished and worked out. Total moduli
space of the BPS non-Abelian walls including all topological sectors is found
to be the complex Grassmann manifold SU(N_F) / [SU(N_C) x SU(N_F-N_C) x U(1)]
endowed with a deformed metric.Comment: 62 pages, 17 figures, the final version in PR
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