10,286 research outputs found

    An Analysis of \pi\pi-Scattering Phase Shift and Existence of \sigma(555) particle

    Full text link
    In most of the Nambu:Jona-Lasinio(NJL)-type models, realizing the hidden chiral symmetry, the existence of a scalar particle \sigma is needed with a mass m_\sigma=2 m_q, as a partner of the Nambu-Goldstone boson \pi. However, the results of many analyses on \pi\pi phase-shift thus far made have been negative for its existence. In this paper we re-analyze the phase-shift, applying a new method, the interfering amplitude method, which treats the T-matrix directly and describes multi-resonances in conformity with the unitarity. As a result, the existence of \sigma has been strongly suggested from the behavior of the \pi\pi-->\pi\pi phase shift between the \pi\pi- and the KK- thresholds, with mass = 553.3 +- 0.5_{st} MeV and width= 242.6 +- 1.2_{st} MeV. The most crucial point in our analysis is the introduction of a negative background phase, possibly reflecting a ``repulsive core" in \pi\pi interactions. The properties of f_0(980) are also investigated from data including those over the KK threshold. Its mass is obtained as 993.2 +- 6.5_{st} +- 6.9_{sys} MeV. Its width is about a hundred MeV, although this depends largely on the treatment of the elasticity and the \pi\pi-->KK phase shift, both of which may have large experimental uncertainties.Comment: 22 pages, Latex with Prog. Theor. Phys. format PTPTEX.sty, 4 EPS figure

    Correlation between Superconducting Transition Temperature TcT_c and Increase of Nuclear Spin-Lattice Relaxation Rate Devided by Temperature 1/T1T1/T_1T at TcT_c in the Hydrate Cobaltate Nax_{x}CoO2β‹…y_{2}\cdot yH2_{2}O

    Full text link
    We have performed Co-nuclear quadrupole resonance (NQR) studies on Nax_{x}CoO2β‹…y_{2}\cdot yH2_{2}O compounds with different Na (xx) and hydrate (yy) contents. Two samples with different Na contents but nearly the same TcT_c values (xx = 0.348, TcT_c = 4.7 K ; xx = 0.339, TcT_c = 4.6 K) were investigated. The spin-lattice relaxation rate 1/T11/T_1 in the superconducting (SC) and normal states is almost the same for the two samples except just above TcT_c. NQR measurements were also performed on different-hydrate-content samples with different TcT_c values, which were prepared from the same Na-content (xx = 0.348) sample. From measurements of 1/T11/T_1 using the different-hydrate-content samples, it was found that a low-TcT_c sample with Tc=3.9T_c = 3.9 K has a larger residual density of states (DOS) in the SC state and a smaller increase of 1/T1T1/T_1T just above TcT_c than a high-TcT_c sample with TcT_c = 4.7 K. The former behavior is consistent with that observed in unconventional superconductors, and the latter suggests the relationship between TcT_c and the increase in DOS just above TcT_c. This increase, which is seemingly associated with the two-dimensionality of the CoO2_2 plane, is considered to be one of the most important factors for the occurrence of superconductivity.Comment: 5 pages, 5 figures, To be published in J. Phys. Soc. Jp

    A Mechanism of Spin-Triplet Superconductivity in Hubbard Model on Triangular La ttice: Application to UNi_2Al_3

    Full text link
    We discuss the possibility of spin-triplet superconductivity in a two-dimensional Hubbard model on a triangular lattice within the third-order perturbation theory. When we vary the symmetry in the dispersion of the bare energy band from D_2 to D_6, spin-singlet superconductivity in the D_2-symmetric system is suppressed and we obtain spin-triplet superconductivity in near the D_6-symmetric system. In this case, it is found that the vertex terms, which are not included in the interaction mediated by the spin fluctuation, are essential for realizing the spin-triplet pairing. We point out the possibility that obtained results correspond to the difference between the superconductivity of UNi_2Al_3 and that of UPd_2Al_3.Comment: 11pages, 5figure

    Potential Profiling of the Nanometer-Scale Charge Depletion Layer in n-ZnO/p-NiO Junction Using Photoemission Spectroscopy

    Full text link
    We have performed a depth-profile analysis of an all-oxide p-n junction diode n-ZnO/p-NiO using photoemission spectroscopy combined with Ar-ion sputtering. Systematic core-level shifts were observed during the gradual removal of the ZnO overlayer, and were interpreted using a simple model based on charge conservation. Spatial profile of the potential around the interface was deduced, including the charge-depletion width of 2.3 nm extending on the ZnO side and the built-in potential of 0.54 eV
    • …