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

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

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

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

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

Phase diagram of an impurity in the spin-1/2 chain: two channel Kondo effect versus Curie law

We consider a magnetic s=1/2 impurity in the antiferromagnetic spin chain as a function of two coupling parameters: the symmetric coupling of the impurity to two sites in the chain $J_1$ and the coupling between the two sites $J_2$. By using field theory arguments and numerical calculations we can identify all possible fixed points and classify the renormalization flow between them, which leads to a non-trivial phase diagram. Depending on the detailed choice of the two (frustrating) coupling strengths, the stable phases correspond either to a decoupled spin with Curie law behavior or to a non-Fermi liquid fixed point with a logarithmically diverging impurity susceptibility as in the two channel Kondo effect. Our results resolve a controversy about the renormalization flow.Comment: 5 pages in revtex format including 4 embedded figures (using epsf). The latest version in PDF format is available from http://fy.chalmers.se/~eggert/papers/phase-diagram.pd

Effect of Inter-Site Repulsions on Magnetic Susceptibility of One-Dimensional Electron Systems at Quarter-Filling

The temperature dependence of the magnetic susceptibility, \chi (T), is investigated for one-dimensional interacting electron systems at quarter-filling within the Kadanoff-Wilson renormalization-group method. The forward scattering on the same branch (the g_4-process) is examined together with the backward (g_1) and forward (g_2) scattering amplitudes on opposite branches. In connection with lattice models, we show that \chi (T) is strongly enhanced by the nearest-neighbor interaction, an enhancement that surpasses one of the next-nearest-neighbor interaction. A connection between our predictions for \chi (T) and experimental results for \chi (T) in quasi-one-dimensional organic conductors is presented.Comment: 4 pages, 4 figures, to be published in Journal of the Physical Society of Japan, vol. 74, No. 1

Doped coupled frustrated spin-1/2 chains with four-spin exchange

The role of various magnetic inter-chain couplings is investigated by numerical methods in doped frustrated quantum spin chains. A non-magnetic dopant introduced in a gapped spin chain releases a free spin-1/2 soliton. The formation of a local magnetic moment is analyzed in term of soliton confinement. A four-spin coupling which might originate from cyclic exchange is shown to produce such a confinement in contrast to transverse magnetic exchange. Dopants on different chains experience an effective space-extended non-frustrating pairwise spin interaction.Comment: Few modifications and references added. Submitted to PR

Possible Localized Modes in the Uniform Quantum Heisenberg Chains of Sr2CuO3

A model of mobile-bond defects is tentatively proposed to analyze the "anomalies" observed on the NMR spectrum of the quantum Heisenberg chains of Sr2CuO3. A bond-defect is a local change in the exchange coupling. It results in a local alternating magnetization (LAM), which when the defect moves, creates a flipping process of the local field seen by each nuclear spin. At low temperature, when the overlap of the LAM becomes large, the defects form a periodic structure, which extends over almost all the chains. In that regime, the density of bond-defects decreases linearly with T.Comment: 4 pages + 3 figures. To appear in Physical Review