Ground state of the three-band Hubbard model

The ground state of the two-dimensional three-band Hubbard model in oxide superconductors is investigated by using the variational Monte Carlo method. The Gutzwiller-projected BCS and spin- density wave (SDW) functions are employed in the search for a possible ground state with respect to dependences on electron density. Antiferromagnetic correlations are considerably enhanced near half-filling. It is shown that the d-wave state may exist away from half-filling for both the hole and electron doping cases. The overall structure of the phase diagram obtained by the calculations qualitatively agrees with experimental indications. The superconducting condensation energy is in reasonable agreement with the experimental value obtained from specific heat and critical magnetic field measurements for optimally doped samples. The inhomogeneous SDW state is also examined near 1/8-hole doping.Comment: 10 pages, 17 figure

Search for Photon-Photon Elastic Scattering in the X-ray Region

We report the first results of a search for real photon-photon scattering using X rays. A novel system is developed to split and collide X-ray pulses by applying interferometric techniques. A total of $6.5\times10^{5}$ pulses (each containing about $10^{11}$ photons) from an X-ray Free-Electron Laser are injected into the system. No scattered events are observed, and an upper limit of $1.7\times 10^{-24}$ ${\rm m^{2}}$ (95% C.L.) is obtained on the photon-photon elastic scattering cross section at 6.5 keV

Sign reversals of the Quantum Hall Effect in quasi-1D conductors

The sign reversals of the Quantum Hall Effect observed in quasi-one-dimensional conductors of the Bechgaard salts family are explained within the framework of the quantized nesting model. The sequence of reversals is driven by slight modifications of the geometry of the Fermi surface. It is explained why only even phases can have signign reversals and why negative phases are less stable than positive ones.Comment: 4 LaTex pages, 3 Postscript figure

t'- and t"-dependence of the bulk-limit superconducting condensation energy of the 2D Hubbard model

The 2D Hubbard model having the 2nd- and 3rd-neighbor transfer energies t' and t" is investigated by use of the variational Monte Carlo method. At the nearly optimal doping with on-site Coulomb energy U=6 (energy unit is t) the condensation energy Econd for the d-wave superconductivity (SC) is computed for lattices of sizes from 10x10 to 28x28 with the aim to get its bulk-limit value. t" is fixed at -t'/2. Outside and in the neighborhood of the SDW region of -0.16=<t'=<-0.08 the SC Econd dominates over the SDW Econd. At t'=-0.05 and -0.10 we obtained a definitely finite bulk-limit SC Econd of the order of the experimental value for YBCO. At t'=0 Econd nearly vanishes. For t'=<-0.18, the SC Econd strongly oscillates as a function of the lattice size, when periodic boundary conditions (b.c.'s) are imposed to both axes. In the case of periodic and antiperiodic b.c.'s, a finite bulk-limit value is obtained at t'=-0.22. Econd tends to vanish with further decrease of t'. With our results the SC of LSCO is understandable with t'~ -0.10. The t' values of Hg1201, Tl2201 and Na-CCOC seem close to -0.20 so that they locate in the boundary zone of SC indicated in the present work. Slightly larger U improves the situation by increasing Econd.Comment: 12 pages, 6 figures, ISS2007 Proc. (Physica C

Search for Axion like particles using Laue-case conversion in a single crystal

Axion Like Particles (ALPs) with a sub-keV range mass are searched by using the light-shining-through-a-wall technique. A novel system is developed in which injected X rays are converted and reconverted by the Laue-case conversion within a silicon single crystal with dual blades. The resonant ALPs' mass of the conversion is scanned by varying the X-ray injection angle to the crystal. No significant signals are observed, and 90% C. L. upper limits on the ALP-two photon coupling constant are obtained as follows, g_{a\gamma\gamma} < 4.2 \times 10^{-3} GeV^{-1} (m_a < 10 eV), g_{a\gamma\gamma} < 5.0 \times 10^{-3} GeV^{-1} (46 eV < m_a < 1020 eV). These are the most stringent laboratorial constraints on ALPs heavier than 300 eV.Comment: 13 pages, 5 figures, 1 tabl

VEGF (Vascular Endothelial Growth Factor) Induces NRP1 (Neuropilin-1) Cleavage via ADAMs (a Disintegrin and Metalloproteinase) 9 and 10 to Generate Novel Carboxy- Terminal NRP1 Fragments That Regulate Angiogenic Signaling

OBJECTIVE: NRP1(neuropilin-1) acts as a coreceptor for VEGF (vascular endothelial growth factor) with an essential role in angiogenesis. Recent findings suggest that posttranslational proteolytic cleavage of VEGF receptors may be an important mechanism for regulating angiogenesis, but the role of NRP1 proteolysis and the NRP1 species generated by cleavage in endothelial cells is not known. To characterize NRP1 proteolytic cleavage in endothelial cells, determine the mechanism, and investigate the role of NRP1 cleavage in regulation of endothelial cell function. APPROACH AND RESULTS: NRP1 species comprising the carboxy (C)-terminal and transmembrane NRP1 domains but lacking the ligand-binding A and B regions are constitutively expressed in endothelial cells. Generation of these C-terminal domain NRP1 proteins is upregulated by phorbol ester and Ca2+ ionophore, and reduced by pharmacological inhibition of metalloproteinases, by small interfering RNA-mediated knockdown of 2 members of ADAM (a disintegrin and metalloproteinase) family, ADAMs 9 and 10, and by a specific ADAM10 inhibitor. Furthermore, VEGF upregulates expression of these NRP1 species in an ADAM9/10-dependent manner. Transduction of endothelial cells with adenoviral constructs expressing NRP1 C-terminal domain fragments inhibited VEGF-induced phosphorylation of VEGFR2 (VEGF receptor tyrosine kinase)/KDR and decreased VEGF-stimulated endothelial cell motility and angiogenesis in coculture and aortic ring sprouting assays. CONCLUSIONS: These findings identify novel NRP1 species in endothelial cells and demonstrate that regulation of NRP1 proteolysis via ADAMs 9 and 10 is a new regulatory pathway able to modulate VEGF angiogenic signaling

Spin-Density-Wave Phase Transitions in Quasi-One-Dimensional Dimerized Quarter-Filled Organic Conductors

We have studied spin density wave (SDW) phase transitions in dimerized quarter-filled Hubbard chains weakly coupled via interchain one-particle hopping, $t_{b0}$. It is shown that there exists a critical value of $t_{b0}$, $t_{b}^\ast$, between the incoherent metal regime ($t_{b0}<t_{b}^\ast$) and the Fermi liquid regime ($t_{b0}>t_{b}^\ast$) in the metallic phase above the SDW transition temperature. By using the 2-loop perturbative renormalization-group approach together with the random-phase-approximation, we propose a SDW phase diagram covering both of the regimes. The SDW phase transition from the incoherent metal phase for $t_{b0}<t_{b}^\ast$ is caused by growth of the intrachain electron-electron umklapp scattering toward low temperatures, which is regarded as preformation of the Mott gap. We discuss relevance of the present result to the SDW phase transitions in the quasi-one-dimensional dimerized quarter-filled organic conductors, (TMTTF)$_2$X and (TMTSF)$_2$X.Comment: 19 pages, 13 eps figures, uses jpsj.sty, corrected typo in the text and figures, no changes to the paper, to appear in J. Phys. Soc. Jpn. 68, No.8 (1999

Stripe formation in high-Tc superconductors

The non-uniform ground state of the two-dimensional three-band Hubbard model for the oxide high-Tc superconductors is investigated using a variational Monte Carlo method. We examine the effect produced by holes doped into the antiferromagnetic (AF) background in the underdoped region. It is shown that the AF state with spin modulations and stripes is stabilized du to holes travelling in the CuO plane. The structures of the modulated AF spins are dependent upon the parameters used in the model. The effect of the boundary conditions is reduced for larger systems. We show that there is a region where incommensurability is proportional to the hole density. Our results give a consistent description of stripes observed by the neutron- scattering experiments based on the three-band model for CuO plane.Comment: 8 pages, 9 figure