5,248 research outputs found
Reply to the "Comment on 'Phase diagram of an impurity in the spin-1/2 chain: two channel Kondo effect versus Curie law'"
In a comment by A.A. Zvyagin the phase diagram in our Letter [Phys. Rev.
Lett. 86, 516 (2001)] was critisized of being incomplete and a new fixed point
was suggested. We show that this point is in fact not a fixed point and that
the phase diagram is correct as presented.Comment: Reply to a comment by A.A. Zvyagin. 1 page, 1 figure. The latest
version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/reply.pd
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
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]
How to treat benchmark revisions? The case of German production and orders statistics
Elements of an econometric examination of benchmark revisions in real-time data are suggested. Structural break tests may be applied to detect heterogeneities within vintages. Systems cointegration tests are helpful to reveal inconsistencies across vintages. Differencing and rebasing, often used to adjust for benchmark revisions, are generally not sufficient to ensure consistent real-time macroeconomic data. Vintage transformation functions estimated by cointegrating regressions are more flexible. Inappropriate conversion may cause observed revision statistics to be affected by nuisance parameters. In German industrial production and orders statistics, remaining revisions are generally biased and serially correlated. --real-time data,benchmark revisions,industrial production,orders
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
Wigner crystal vs. Friedel oscillations in the 1D Hubbard model
We analyze the fermion density of the one-dimensional Hubbard model using
bosonization and numerical DMRG calculations. For finite systems we find a
relatively sharp crossover even for moderate short range interactions into a
region with density waves as a function of density. The results show
that the unstable fixed point of a spin-incoherent state can dominate the
physical behavior in a large region of parameter space in finite systems. The
crossover may be observable in ultra cold fermionic gases in optical lattices
and in finite quantum wires.Comment: 6 pages, 6 figures. Published version. The most recent file can be
found at http://www.physik.uni-kl.de/eggert/papers/index.htm
A stochastical model for periodic domain structuring in ferroelectric crystals
A stochastical description is applied in order to understand how
ferroelectric structures can be formed. The predictions are compared with
experimental data of the so-called electrical fixing: Domains are patterned in
photorefractive lithium niobate crystals by the combination of light-induced
space-charge fields with externally applied electrical fields. In terms of our
stochastical model the probability for domain nucleation is modulated according
to the sum of external and internal fields. The model describes the shape of
the domain pattern as well as the effective degree of modulation
- …