5,247 research outputs found
Edge Logarithmic Corrections probed by Impurity NMR
Semi-infinite quantum spin chains display spin autocorrelations near the
boundary with power-law exponents that are given by boundary conformal field
theories. We show that NMR measurements on spinless impurities that break a
quantum spin chain lead to a spin-lattice relaxation rate 1/T_1^edge that has a
temperature dependence which is a direct probe of the anomalous boundary
exponents. For the antiferromagnetic S=1/2 spin chain, we show that 1/T_1^edge
behaves as T (log T)^2 instead of (log T)^1/2 for a bulk measurement. We show
that, in the case of a one-dimensional conductor described by a Luttinger
liquid, a similar measurement leads to a relaxation rate 1/T_1^{edge} behaving
as T, independent of the anomalous exponent K_rho.Comment: 4 pages, 1 encapsulated figure, corrected typo
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
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
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
Universal cross-over behavior of a magnetic impurity and consequences for doping in spin-1/2 chains
We consider a magnetic impurity in the antiferromagnetic spin-1/2 chain which
is equivalent to the two-channel Kondo problem in terms of the field
theoretical description. Using a modification of the transfer-matrix density
matrix renormalization group (DMRG) we are able to determine local and global
properties in the thermodynamic limit. The cross-over function for the impurity
susceptibility is calculated over a large temperature range, which exhibits
universal data-collapse. We are also able to determine the local
susceptibilities near the impurity, which show an interesting competition of
boundary effects. This results in quantitative predictions for experiments on
doped spin-1/2 chains, which could observe two-channel Kondo physics directly.Comment: 5 pages in revtex format including 3 embedded figures (using epsf).
The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/crossover.pdf . Accepted by PR
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