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

Recursive Method for the Density of States in One Dimension

We derive a powerful yet simple method for analyzing the local density of states in gapless one dimensional fermionic systems, including extensions such as momentum dependent interaction parameters and hard-wall boundaries. We study the crossover of the local DOS from individual density waves to the well-known asymptotic powerlaws and identify characteristic signs of spin charge separation in possible STM experiments. For semi-infinite systems a closed analytic expression is found in terms of hypergeometric functions.Comment: 5 pages and 3 figures. The latest version can be found at http://www.physik.uni-kl.de/eggert/papers/index.htm

Design and evaluation of low cost blades for large wind driven generating systems

The development and evaluation of a low cost blade concept based on the NASA-Lewis specifications is discussed. A blade structure was designed and construction methods and materials were selected. Complete blade tooling concepts, various technical and economic analysis, and evaluations of the blade design were performed. A comprehensive fatigue test program was conducted to provide data and to verify the design. A test specimen of the spar assembly, including the root end attachment, was fabricated. This is a full-scale specimen of the root end configuration, 20 ft long. A blade design for the Mod '0' system was completed

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 KCuF3_3

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$_3$. 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

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

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

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]