2,704 research outputs found
Impurities in S=1/2 Heisenberg Antiferromagnetic Chains: Consequences for Neutron Scattering and Knight Shift
Non-magnetic impurities in an S=1/2 Heisenberg antiferromagnetic chain are
studied using boundary conformal field theory techniques and finite-temperature
quantum Monte Carlo simulations. We calculate the static structure function,
S_imp(k), measured in neutron scattering and the local susceptibility, chi_i
measured in Knight shift experiments. S_imp(k) becomes quite large near the
antiferromagnetic wave-vector, and exhibits much stronger temperature
dependence than the bulk structure function. \chi_i has a large component which
alternates and increases as a function of distance from the impurity.Comment: 8 pages (revtex) + one postscript file with 6 figures. A complete
postscript file with all figures + text (10pages) is available from
http://fy.chalmers.se/~eggert/struct.ps or by request from
[email protected] Submitted to Phys. Rev. Let
Local Magnetic Susceptibility of the Positive Muon in the Quasi 1D S=1/2 Antiferromagnet KCuF
We report muon spin rotation measurements of the local magnetic
susceptibility around a positive muon in the paramagnetic state of the quasi
one-dimensional spin 1/2 antiferromagnet KCuF. Signals from two distinct
sites are resolved which have a temperature dependent frequency shift which is
different than the magnetic susceptibility. This difference is attributed to a
muon induced perturbation of the spin 1/2 chain.Comment: 13 pages, 4 figures, The 2002 International Conference on Muon Spin
Rotation, Relaxation and Resonance, Virginia. US
Neel order in doped quasi one-dimensional antiferromagnets
We study the Neel temperature of quasi one-dimensional S=1/2 antiferromagnets
containing non-magnetic impurities. We first consider the temperature
dependence of the staggered susceptibility of finite chains with open boundary
conditions, which shows an interesting difference for even and odd length
chains. We then use a mean field theory treatment to incorporate the three
dimensional inter-chain couplings. The resulting Neel temperature shows a
pronounced drop as a function of doping by up to a factor of 5.Comment: 4 pages in revtex4 format including 2 epsf-embedded figures. The
latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/staggered.pd
Lattice vs. continuum theory of the periodic Heisenberg chain
We consider the detailed structure of low energy excitations in the periodic
spin-1/2 XXZ Heisenberg chain. By performing a perturbative calculation of the
non-linear corrections to the Gaussian model, we determine the exact
coefficients of asymptotic expansions in inverse powers of the system length N
for a large number of low-lying excited energy levels. This allows us to
calculate eigenenergies of the lattice model up to order order N^-4, without
having to solve the Bethe Ansatz equations. At the same time, it is possible to
express the exact eigenstates of the lattice model in terms of bosonic modes.Comment: 17 pages, 8 Figures. The latest version can be found at
http://www.physik.uni-kl.de/eggert/papers/index.htm
Numerical Evidence for Multiplicative Logarithmic Corrections from Marginal Operators
Field theory calculations predict multiplicative logarithmic corrections to
correlation functions from marginally irrelevant operators. However, for the
numerically most suitable model - the spin-1/2 chain - these corrections have
been controversial. In this paper, the spin-spin correlation function of the
antiferromagnetic spin-1/2 chain is calculated numerically in the presence of a
next nearest neighbor coupling J2 for chains of up to 32 sites. By varying the
coupling strength J2 we can control the effect of the marginal operator, and
our results unambiguously confirm the field theory predictions. The critical
value at which the marginal operator vanishes has been determined to be at J2 =
0.241167 +/- 0.000005J.Comment: revised paper with extended data-analysis. 5 pages, using revtex with
4 embedded figures (included with macro). A complete postscript file with all
figures + text (5 pages) is available from
http://FY.CHALMERS.SE/~eggert/marginal.ps or by request from
[email protected]
Spin- and charge-density oscillations in spin chains and quantum wires
We analyze the spin- and charge-density oscillations near impurities in spin
chains and quantum wires. These so-called Friedel oscillations give detailed
information about the impurity and also about the interactions in the system.
The temperature dependence of these oscillations explicitly shows the
renormalization of backscattering and conductivity, which we analyze for a
number of different impurity models. We are also able to analyze screening
effects in one dimension. The relation to the Kondo effect and experimental
consequences are discussed.Comment: Final published version. 15 pages in revtex format including 22
epsf-embedded figures. The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/density-osc.pd
Chain breaks and the susceptibility of Sr_2Cu_{1-x}Pd_xO_{3+\delta} and other doped quasi one-dimensional antiferromagnets
We study the magnetic susceptibility of one-dimensional S=1/2
antiferromagnets containing non-magnetic impurities which cut the chain into
finite segments. For the susceptibility of long anisotropic Heisenberg
chain-segments with open boundaries we derive a parameter-free result at low
temperatures using field theory methods and the Bethe Ansatz. The analytical
result is verified by comparing with Quantum-Monte-Carlo calculations. We then
show that the partitioning of the chain into finite segments can explain the
Curie-like contribution observed in recent experiments on
Sr_2Cu_{1-x}Pd_xO_{3+\delta}. Possible additional paramagnetic impurities seem
to play only a minor role.Comment: 4 pages, 3 figures, final versio
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