1,255 research outputs found
Spin-spin correlations between two Kondo impurities coupled to an open Hubbard chain
In order to study the interplay between Kondo and
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, we calculate the spin-spin
correlation functions between two Kondo impurities coupled to different sites
of a half-filled open Hubbard chain. Using the density-matrix renormalization
group (DMRG), we re-examine the exponents for the power-law decay of the
correlation function between the two impurity spins as a function of the
antiferromagnetic coupling J, the Hubbard interaction U, and the distance R
between the impurities. The exponents for finite systems obtained in this work
deviate from previously published DMRG calculations. We furthermore show that
the long-distance behavior of the exponents is the same for impurities coupled
to the bulk or to both ends of the chain. We note that a universal exponent for
the asymptotic behavior cannot be extracted from these finite-size systems with
open boundary conditions.Comment: 8 pages, 10 figures; v2: final version, references and Fig. 8 adde
Spin-orbit coupling and electron spin resonance for interacting electrons in carbon nanotubes
We review the theoretical description of spin-orbit scattering and electron
spin resonance in carbon nanotubes. Particular emphasis is laid on the effects
of electron-electron interactions. The spin-orbit coupling is derived, and the
resulting ESR spectrum is analyzed both using the effective low-energy field
theory and numerical studies of finite-size Hubbard chains and two-leg Hubbard
ladders. For single-wall tubes, the field theoretical description predicts a
double peak spectrum linked to the existence of spin-charge separation. The
numerical analysis basically confirms this picture, but also predicts
additional features in finite-size samples.Comment: 19 pages, 4 figures, invited review article for special issue in J.
Phys. Cond. Mat., published versio
Paper Session I-C - Non-Destructive Detection of Corrosion Under Paint on Critical Surfaces
We describe our proof-of-concept demonstration of the well-known thermal diffusion imaging technique *\u3e 2\u3e3 for detection of corrosion under paint on critical surfaces. Our first application will be the detection and mapping of corrosion on arbiter vehicle wing spars and rudder speed brakes. The technique will also used for the evaluation of doubler plate bond integrity on the rudder speed brakes
NMR relaxation rates for the spin-1/2 Heisenberg chain
The spin-lattice relaxation rate and the spin echo decay rate
for the spin- antiferromagnetic Heisenberg chain are
calculated using quantum Monte Carlo and maximum entropy analytic continuation.
The results are compared with recent analytical calculations by Sachdev. If the
nuclear hyperfine form factor is strongly peaked around the
predicted low-temperature behavior [, ] extends up to temperatures as high as . If has significant weight for there are large
contributions from diffusive long-wavelength processes not taken into account
in the theory, and very low temperatures are needed in order to observe the
asymptotic forms.Comment: 9 pages, Revtex 3.0, 5 uuencoded ps figures To appear in Phys. Rev.
B, Rapid Com
Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5)
We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.Comment: 5 pages, 4 figures include
Spin-orbit coupling and ESR theory for carbon nanotubes
A theoretical description of ESR in 1D interacting metals is given, with
primary emphasis on carbon nanotubes. The spin-orbit coupling is derived, and
the resulting ESR spectrum is analyzed by field theory and exact
diagonalization. Drastic differences in the ESR spectra of single-wall and
multi-wall nanotubes are found. For single-wall tubes, the predicted double
peak spectrum could reveal spin-charge separation.Comment: 4 pages, 1 figure, final version to appear in PR
Paper Session III-B - Ultrasonic Correlation Bolt Tension Analyzer
We describe our efforts in the development of an improved ultrasonic bolt tension analyzer (bolt gage) for use in precision tensioning of bolts in critical applications. This new instrument uses correlation techniques to ameliorate the peak jumping problems usually associated with ultrasonic bolt gages. Our instrument has been put through substantial (though not exhaustive) tests, with very good results
Shadow band in the one-dimensional large Hubbard model
We show that the factorized wave-function of Ogata and Shiba can be used to
calculate the dependent spectral functions of the one-dimensional, infinite
Hubbard model, and of some extensions to finite . The resulting spectral
function is remarkably rich: In addition to low energy features typical of
Luttinger liquids, there is a well defined band, which we identify as the
shadow band resulting from spin fluctuations. This band should be
detectable experimentally because its intensity is comparable to that of the
main band for a large range of momenta.Comment: Latex file. 4 pages. Figures upon reques
Spectral functions of the 1D Hubbard model in the U -> \infty limit: How to use the factorized wave-function
We give the details of the calculation of the spectral functions of the 1D
Hubbard model using the spin-charge factorized wave-function for several
versions of the U -> +\infty limit. The spectral functions are expressed as a
convolution of charge and spin dynamical correlation functions. A procedure to
evaluate these correlation functions very accurately for large systems is
developed, and analytical results are presented for the low energy region.
These results are fully consistent with the conformal field theory. We also
propose a direct method of extracting the exponents from the matrix elements in
more general cases.Comment: 15 pages,7 eps figures, RevTeX, needs epsf and multico
Phase diagram of the extended Hubbard chain with charge-dipole interactions
We consider a modified extended Hubbard model (EHM) which, in addition to the
on-site repulsion U and nearest-neighbor repulsion V, includes polarization
effects in second-order perturbation theory. The model is equivalent to an EHM
with renormalized U plus a next-nearest-neighbor repulsion term. Using a method
based on topological quantum numbers (charge and spin Berry phases), we
generalize to finite hopping t the quantum phase diagram in one dimension
constructed by van den Brink et al. (Phys. Rev. Lett. 75, 4658 (1995)). At
hopping t=0 there are two charge density-wave phases, one spin density-wave
phase and one intermediate phase with charge and spin ordering, depending on
the parameter values. At t \neq 0 the nature of each phase is confirmed by
studying correlation functions. However, in addition to the strong-coupling
phases, a small region with bond ordering appears. The region occupied by the
intermediate phase first increases and then decreases with increasing t, until
it finally disappears for t of the order but larger than U. For small t, the
topological transitions agree with the results of second order perturbation
theory.Comment: 6 pages, 5 figures, two columns latex version. Accepted for
publication in Physical Review B. Mistaken reference 16 has been correcte
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