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

Precision orbit computations for an operational environment

Taking advantage of the improvements to the Earth's gravitation field and tracking station coordinates, an orbital computational consistency of the order of 5 meters was achieved for total position differences between orbital solutions for the Seasat and GEOS-3. The main source of error in these solutions was in the mathematical models that are required to generate these results, i.e., gravitation, atmospheric drag, etc. Different Earth gravitation fields and tracking coordinates were analyzed and evaluated in obtaining these computational results. Comparisons and evaluations of the Seasat results were obtained in terms of different solution types such as the Doppler only, Laser only, Doppler and Laser, etc. Other investigation using the Seasat data were made in order to determine their effect on the computational results at this particular level of consistency

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

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

Letters between C. A. Eggert and William Kerr\u27s secretary

Letters concerning position in the modern languages department at Utah Agricultural College being filled

Thermo-mechanical tests with the first wall mock-up TS1

Wissenschaftlicher Bericht - FZKA 6035 Thermomechanische Versuche mit dem First Wall Mock-up TS1 Ein Ausschnitt (Mock-up) der Ersten Wand vom Design für den Next European Torus (NET) stand als wasser-gekühlte Stahl-Struktur für Experimente zur Verfügung. Weil der Mock-up Vorschädigungen durch eine große Zahl von Thermoelement-Bohrungen aufwies, war er nicht für thermische Ermüdungsexperimente vorgesehen; vielmehr wurde er als prototypische Hintergrundstruktur verwendet für thermomechanische Tests mit Schutzziegeln auf Graphit-Basis und deren Haltevorrichtungen. In einer ersten Testreihe wurde die Oberfläche des ungeschützten Mock-ups einer thermischen Last ausgesetzt. Die Vorhersage einer FE Modellrechnung konnte mit Dehnungen, die auf seiner Rückseite gemessen wurden, in vernünftigem Umfang bestätigt werden. In einer zweiten Testreihe wurde der Mock-up mit einem strahlungs-gekühlten Ziegel, der nicht in engem thermischen Kontakt mit dem Mock-up stand, geschützt. Die Tests zeigten, daß es sehr wichtig ist, auf angemessen dimensionierte Spalte zu achten, die Unterschiede in der thermischen Ausdehnung und Verbiegung auch während der thermischen Transienten zulassen. Schließlich wurde der Mock-up mit leitungs-gekühlten Ziegeln, die mit einer Zwischenschicht aus flexiblem Graphit auf den Mock-up gedrückt wurden, geschützt. Die Testergebnisse zeigten, daß der Wärmeübergang an der Kontaktschicht gleichmäßig war und auch nach thermischen Zyklen auf hohem Temperatur-Niveau zuverlässig erhalten blieb

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

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

Quantitative expression of the spin gap via bosonization for a dimerized spin-1/2 chain

Using results on the mass gap in the sine-Gordon model combined with the exact amplitudes in the bosonized representation of the Heisenberg spin-1/2 chain and one-loop renormalization group, we derive a quantitative expression for the gap in a dimerized spin-1/2 chain. This expression is shown to be in good agreement with recent numerical estimates when a marginally irrelevant perturbation is taken into account.Comment: 5 pages, 2 EPS figures, uses svjour.cl