Theory of Low Temperature Electron Spin Resonance in Half-integer Spin Antiferromagnetic Chains

A theory of low temperature (T) electron spin resonance (ESR) in half-integer spin antiferromagnetic chains is developed using field theory methods and avoiding previous approximations. It is compared to experiments on Cu benzoate. Power laws are predicted for the line-width broadening due to various types of anisotropy. At T -> 0, zero width absorption peaks occur in some cases. The second ESR peak in Cu benzoate, observed at T<.76K, is argued not to indicate Neel order as previously claimed, but to correspond to a sine-Gordon "breather" excitation.Comment: 4 pages, REVTEX, 3 PostScript figures embedded in tex

Boundary Critical Phenomena in SU(3) "Spin" Chains

SU(3)-invariant "spin" chains with a single impurity, such as a modified exchange coupling on one link, are analyzed using boundary conformal field theory techniques. These chains are equivalent to a special case of the "tJV" model, i.e. the t-J model with a nearest neighbour repulsion added. In the continuum limit they are equivalent to two free bosons at a special value of the compactification radii. The SU(3) symmetry, which is made explicit in this formulation, provides insight into the exact solution of a non-trivial boundary critical point found earlier in another formulation of this model as a theory of quantum Brownian motion.Comment: 19 pages, Rev Te

Exact Analysis of ESR Shift in the Spin-1/2 Heisenberg Antiferromagnetic Chain

A systematic perturbation theory is developed for the ESR shift and is applied to the spin-1/2 Heisenberg chain. Using the Bethe ansatz technique, we exactly analyze the resonance shift in the first order of perturbative expansion with respect to an anisotropic exchange interaction. Exact result for the whole range of temperature and magnetic field, as well as asymptotic behavior in the low-temperature limit are presented. The obtained g-shift strongly depends on magnetic fields at low temperature, showing a significant deviation from the previous classical result.Comment: 4 pages, 3 figures,to be published in Phys. Rev. Let

Rescue with an anti-inflammatory peptide of chickens infected H5N1 avian flu

Chickens suffering from avian flu caused by H5N1 influenza virus are destined to die within 2 days due to a systemic inflammatory response. Since HVJ infection (1,2) and influenza virus infection (3,4) cause infected cells to activate homologous serum complement, the systemic inflammatory response elicited could be attributed to the unlimited generation of C5a anaphylatoxin of the complement system, which is a causative peptide of serious inflammation. In monkeys inoculated with a lethal dose of LPS (4 mg/kg body weight), inhibition of C5a by an inhibitory peptide termed AcPepA (5) rescued these animals from serious septic shock which would have resulted in death within a day (6). Therefore, we tested whether AcPepA could also have a beneficial effect on chickens with bird flu. On another front, enhanced production of endothelin-1 (ET-1) and the activation of mast cells (MCs) have been implicated in granulocyte sequestration (7). An endothelin receptor derived antisense homology box peptide (8) designated ETR-P1/fl was shown to antagonize endothelin A receptor (ET-A receptor) (9) and reduce such inflammatory responses as endotoxin-shock (10) and hemorrhagic shock (11), thereby suppressing histamine release in the circulation (12). Thus, we also administered ETR-P1/fl to bird flu chickens expecting suppression of a systemic inflammatory response

Non-Commutative Instantons and the Seiberg-Witten Map

We present several results concerning non-commutative instantons and the Seiberg-Witten map. Using a simple ansatz we find a large new class of instanton solutions in arbitrary even dimensional non-commutative Yang-Mills theory. These include the two dimensional ``shift operator'' solutions and the four dimensional Nekrasov-Schwarz instantons as special cases. We also study how the Seiberg-Witten map acts on these instanton solutions. The infinitesimal Seiberg-Witten map is shown to take a very simple form in operator language, and this result is used to give a commutative description of non-commutative instantons. The instanton is found to be singular in commutative variables.Comment: 26 pages, AMS-LaTeX. v2: the formula for the commutative description of the Nekrasov-Schwarz instanton corrected (sec. 4). v3: minor correction

Multipole State of Heavy Lanthanide Filled Skutterudites

We discuss multipole properties of filled skutterudites containing heavy lanthanide Ln from a microscopic viewpoint on the basis of a seven-orbital Anderson model. For Ln=Gd, in contrast to naive expectation, quadrupole moments remain in addition to main dipole ones. For Ln=Ho, we find an exotic state governed by octupole moment. For Ln=Tb and Tm, no significant multipole moments appear at low temperatures, while for Ln=Dy, Er, and Yb, dipole and higher-order multipoles are dominant. We briefly discuss possible relevance of these multipole states with actual materials.Comment: 5 pages, 3 figure

Multipole as ff-Electron Spin-Charge Density in Filled Skutterudites

It is shown that $f$-electron multipole is naturally defined as spin-charge one-electron density operator in the second-quantized form with the use of tensor operator on the analogy of multipole expansion of electromagnetic potential from charge distribution in electromagnetism. Due to this definition of multipole, it is possible to determine multipole state from a microscopic viewpoint on the basis of the standard linear response theory for multipole susceptibility. In order to discuss multipole properties of filled skutterudites, we analyze a seven-orbital impurity Anderson model by employing a numerical renormalization group method. We show our results on possible multipole states of filled skutterudite compounds.Comment: To appear in the Proceedings of International Conference on "New Quantum Phenomena in Skutterudite and Related Systems" (September 2007, Kobe, Japan

Pressure effects on an organic radical ferromagnet: 2,5-difluorophenyl-a-nitronyl nitroxide

Raising a transition temperature (Tc) in organic radical ferromagnets is a desire for material scientists. We investigated the pressure effects on an organic radical ferromagnet 2,5-difluorophenyl-α-nitronyl nitroxide (2,5-DFPNN), which has a ferromagnetic transition at 0.45 K. The hydrostatic pressure effects were investigated through measurements of ac magnetic susceptibility (χ) up to P=1.7GPa, heat capacity (Cp) up to P=1.5GPa, and powder x-ray diffraction up to P=4.7GPa. Furthermore, ac magnetic susceptibility under nonhydrostatic pressure was also measured in the pressure region up to 10.0 GPa. As for 2,5-DFPNN, we observed the pressure-induced enhancement of Tc as dTc/dP=7.9×10−2K/GPa [Tc(P=1.5GPa)=0.57K], while other prototypes, the β phase of p-NPNN and p−Cl−C6H4−CH=N−TEMPO show the negative pressure effects. The results for the Cp and the crystal structural analysis suggest that the magnetic dimension of the short-range order developing above Tc transforms from one dimension (a axis) to two dimensions (ac plane) under high pressure. This increase of the magnetic dimension probably promotes to increase Tc. The ferromagnetic signal of χ, however, decreases with increasing pressure, and finally disappears for P>~5.0GPa. The decrease seems to originate from the decrease of the ferromagnetic interaction along the b axis. Similar instability of organic ferromagnetic long range order against pressure has been observed for the β phase of p-NPNN and p−Cl−C6H4−CH=N−TEMPO

Contrasting Pressure Effects in Sr2VFeAsO3 and Sr2ScFePO3

We report the resistivity measurements under pressure of two Fe-based superconductors with a thick perovskite oxide layer, Sr2VFeAsO3 and Sr2ScFePO3. The superconducting transition temperature Tc of Sr2VFeAsO3 markedly increases with increasing pressure. Its onset value, which was Tc{onset}=36.4 K at ambient pressure, increases to Tc{onset}=46.0 K at ~4 GPa, ensuring the potential of the "21113" system as a high-Tc material. However, the superconductivity of Sr2ScFePO3 is strongly suppressed under pressure. The Tc{onset} of ~16 K decreases to ~5 K at ~4 GPa, and the zero-resistance state is almost lost. We discuss the factor that induces this contrasting pressure effect.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jpn. No.12 (2009

Pressure Dependence of Superconducting Transition Temperature on Perovskite-Type Fe-Based Superconductors and NMR Study of Sr2VFeAsO3

We report the pressure dependences of the superconducting transition temperature (T_c) in several perovskite-type Fe-based superconductors through the resistivity measurements up to ~4 GPa. In Ca_4(Mg,Ti)_3Fe_2As_2O_y with the highest T_c of 47 K in the present study, the T_c keeps almost constant up to ~1 GPa, and starts to decrease above it. From the comparison among several systems, we obtained a tendency that low T_c with the longer a-axis length at ambient pressure increases under pressure, but high T_c with the shorter a-axis length at ambient pressure hardly increases. We also report the ^75As-NMR results on Sr_2VFeAsO_3. NMR spectrum suggests that the magnetic ordering occurs at low temperatures accompanied by some inhomogeneity. In the superconducting state, we confirmed the anomaly by the occurrence of superconductivity in the nuclear spin lattice relaxation rate 1/T_1, but the spin fluctuations unrelated with the superconductivity are dominant. It is conjectured that the localized V-3d moments are magnetically ordered and their electrons do not contribute largely to the Fermi surface and the superconductivity in Sr_2VFeAsO_3.Comment: 7 pages, 9 figure