Neutron-spin resonance in the optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta

We use inelastic neutron scattering to probe magnetic excitations of an optimally electron-doped superconductor Nd1.85Ce0.15CuO4-delta above and below its superconducting transition temperature Tc=25 K. In addition to gradually opening a spin pseudogap at the antiferromagnetic ordering wave vector Q=(1/2,1/2,0), the effect of superconductivity is to form a resonance centered also at Q=(1/2,1/2,0) but at energies above the spin pseudogap. The intensity of the resonance develops like a superconducting order parameter, similar to those for hole-doped superconductors and electron-doped Pr0.88LaCe0.12CuO4. The resonance is therefore a general phenomenon of cuprate superconductors, and must be fundamental to the mechanism of high-Tc superconductivity.     

MODULATION OF 8-METHOXYPSORALEN-DNA PHOTOADDUCT FORMATION BY CELL DIFFERENTIATION, MITOGENIC STIMULATION AND PHORBOL ESTER EXPOSURE IN MURINE T LYMPHOCYTES

Abstract The effects of cell differentiation and mitogen and phorbol ester stimulation on the formation of 8-methoxypsoralen (8-MOP)-DNA photoadducts in murine T lymphocytes were examined using ³H-8-MOP. While there were no significant differences in 8-MOP photoadduct formation among BALB/c thymocytes, splenocytes, splenic T cells and MRL/1pr lymph node cells, BALB/c bone marrow cells showed fewer photoadducts than did the lymphocytes. This suggested that proliferating progenitor cells may be resistant to 8-MOP photoadduct formation. Incubation of purified splenic T cells with lectin mitogens for 2 h or with phorbol 12-myristate 13-acetate (PMA) for 2–43 h resulted in reduction of 8-MOP photoadduct formation in the DNA, whereas 64 h cultivation with these agents augmented the photoadduct formation. The reduction of photoadduct formation induced by phytohemagglutinin was restored by the further addition of a protein kinase C (PKC) inhibitor, H-7, to the culture. Thus, it is assumed that the reduction of adduct formation evoked by mitogens and PMA is mediated in part by the activation of PKC in the cells. On the other hand, the augmentation of the adduct formation induced by the longer-period cultures with mitogens and PMA appeared to be caused by down-regulation of PKC. The present study showed that the stimulatory signals in which PKC is presumably involved affect the ability of cells to form 8-MOP-DNA photoadducts.     

Ferroelectricity and pressure-induced phenomena driven by neutral ionic valence instability of acid-base supramolecules

Supramolecular ferroelectric cocrystals of phenazine (Phz) with chloranilic acid (H(2)ca), bromanilic acid (H(2)ba), and fluoranilic acid (H(2)fa) have been characterized by the interplay between their structural transformations and solid-state acid-base (proton transfer) reactions. At ambient pressure, the Phz-H(2)ca, Phz-H(2)ba, and their deuterated crystals exhibit incomplete proton displacement, which transforms the neutral molecules into semi-ionic at low temperatures below the Curie point (T(c)(IC) < T < T(c)(I)). For the cocrystal of the less acidic H(2)fa, the ferroelectric phase is induced only by applying hydrostatic pressure above ~0.6 GPa. According to the combined studies of temperature-dependent dielectric permittivity and synchrotron X-ray diffraction, it was proved that the ferroelectric (FE-I) phase is always accompanied at lower temperatures by successive phase transitions to the lattice modulated phases with incommensurate periodicities (IC phase, T(c)(II) < T < T(c)(IC)) and with commensurate (2- or 3-fold) periodicities (FE-II or FE-III phase, T < T(c)(II)). Whereas the ground-state structures at ambient pressure are different from one another among the Phz-H(2)ca (FE-II form), Phz-H(2)ba (FE-III form), and Phz-H(2)fa (paraelectric form), their systematic changes under pressure depict a universal pressure-temperature phase diagram. The possible origins of structural changes are assigned to the valence instability and the frustrated Coulomb interactions that induce the charge disproportionation (coexisting neutral ionic) states with the staging spatial orders.     

Colossal magnetoresistance without phase separation: disorder-induced spin glass state and nanometer scale orbital-charge correlation in half doped manganites

The magnetic and electrical properties of high-quality single crystals of A-site disordered (solid solution) Ln0.5Ba0.5MnO3 are investigated near the phase boundary between the spin-glass insulator and colossal-magnetoresistive ferromagnetic metal, locating near Ln=Sm. The temperature dependence of the ac susceptibility and the x-ray diffuse scattering of Eu0.5Ba0.5MnO3 are analyzed in detail. The uniformity of the random potential perturbation in Ln0.5Ba0.5MnO3 crystals with a small bandwidth yields, rather than the phase separation, an homogeneous short ranged charge or orbital order which gives rise to a nearly atomic spin-glass state. Remarkably, this microscopically disordered "charge-exchange-glass" state alone is able to bring forth the colossal magnetoresistance.     

Fermi surface, surface states, and surface reconstruction in Sr2RuO4

The electronic structure of Sr2RuO4 is investigated by high angular resolution ARPES at several incident photon energies. We address the controversial issues of the Fermi surface (FS) topology and the van Hove singularity at the M point, showing that a surface state and the replica of the primary FS due to sqrt[2]xsqrt[2] surface reconstruction are responsible for previous conflicting interpretations. The FS thus determined by ARPES is consistent with the de Haas-van Alphen results, and it provides additional information on the detailed shape of the alpha, beta, and gamma sheets.     

High-pressure hydrothermal crystal growth and multiferroic properties of a perovskite YMnO3

Orthorhombic perovskites RMnO(3) are representative of spin-driven ferroelectrics. When the radius of the rare-earth ion R is smaller than that of Dy, for instance in YMnO(3), the orthorhombic phase becomes metastable at ambient pressure, which impedes the crystal growth; thus, the detailed magnetic and multiferroic properties of the metastable phase have not been characterized. In this work, we successfully obtained single crystals of orthorhombic YMnO(3) using quasi-hydrothermal conditions under a high pressure of 5.5 GPa. Magnetic and dielectric measurements under magnetic fields revealed that the magnetic ground state is the commensurate E-type antiferromagnetic, while a cycloidal spin phase likely coexists in the intermediate temperature range, which enhances the magnetoelectric response to external fields.     

6-O-carboxymethyl-chitin (CM-chitin) as a drug carrier

Gel was prepared from 6-O-carboxymethyl-chitin (CM-chitin) by the addition of iron(III) chloride under mild conditions without any organic solvent. The optimal conditions for the gel formation were 15 to 30 mM iron(III) chloride and 0.5 to 0.8 degree of substitution in CM-chitin. The amounts of bovine serum albumin (BSA) and the anticancer drug doxorubicin (DOX) incorporated into CM-chitin gels were more than 80% and 30%, respectively under the conditions described above. The release of BSA or DOX from the gels was observed to be increased by lysozyme digestion in a time-dependent manner. This result indicates that CM-chitin might prove useful as a carrier gel for the sustained release of drugs and cytokines, including vaccines.     

Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet: Sr2FeMoO6

We propose a measurement setup for detecting quantum noise over a wide frequency range using inelastic transitions in a tunable two-level system as a detector. The frequency-resolving detector consists of a double quantum dot which is capacitively coupled to the leads of a nearby mesoscopic conductor. The inelastic current through the double quantum dot is calculated in response to equilibrium and nonequilibrium current fluctuations in the nearby conductor, including zero-point fluctuations at very low temperatures. As a specific example, the fluctuations across a quantum point contact are discussed.