Energy dependence of K−K^--"pppp" effective potential derived from coupled-channel Green's function

We investigate the energy dependence of a single-channel effective potential between the $K^-$ and the "$pp$"-core nucleus, which can be obtained as an $K^-$-"$pp$" equivalent local potential from a coupled-channel model for $\bar{K}(NN)$-$\pi(\Sigma N)$ systems. It turns out that the imaginary part of the resultant potential near the $\pi \Sigma N$ decay threshold can well approximate the phase space suppression factor of $K^-pp \to \pi \Sigma N$ decay modes. The effects on the pole position of the $\pi(\Sigma N)$ state in the $\pi \Sigma N$ channel are also discussed.Comment: 4 pages, 2 figures, Proceedings of the International Conference on Exotic Atoms and Related Topics (EXA2011), September 5-9, 2011, Wien, Austria, to appear in Hyperfine Interaction

muSR study of the Cu-spin dynamics in the electron-doped high-Tc cuprate of Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4

Effects of the Zn- and Ni-substitution on the Cu-spin dynamics in the electron-doped Pr0.86LaCe0.14Cu1-y(Zn,Ni)yO4+a-d with y = 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content d have been studied using zero-field muon-spin-relaxation (muSR) measurements at temperatures down to 2 K. For the as-grown sample (d = 0, y = 0) and the sample with a very small d value (d < 0.01, y = 0), a muon-spin precession due to long-range antiferromagnetic order has been observed. On the other hand, no precession has been observed for moderately oxygen-reduced samples (0.01 < d < 0.09). It has been found that for all the samples of 0.01 < d < 0.09 the asymmetry A(t) (muSR time spectrum) in the long-time region increases with decreasing temperature at low temperatures, suggesting possible slowing-down of the Cu-spin fluctuations. On the other hand, no significant difference between Zn- and Ni-substitution effects on the slowing down of the Cu-spin fluctuations has been observed.Comment: 4 pages, 2 figures, Proceeding of 10th muSR conference 2005, to be published in Physica

Novel Electronic State and Superconductivity in the Electron-Doped High-Tc T'-Superconductors

In this review article, we show our recent results relating to the undoped (Ce-free) superconductivity in the electron-doped high-Tc cuprates with the so-called T' structure. For an introduction, we briefly mention the characteristics of the electron-doped T'-cuprates, including the reduction annealing, conventional phase diagram and undoped superconductivity. Then, our transport and magnetic results and results relating to the superconducting pairing symmetry of the undoped and underdoped T'-cuprates are shown. Collaborating spectroscopic and nuclear magnetic resonance results are also shown briefly. It has been found that, through the reduction annealing, a strongly localized state of carriers accompanied by an antiferromagnetic pseudogap in the as-grown samples changes to a metallic and superconducting state with a short-range magnetic order in the reduced superconducting samples. The formation of the short-range magnetic order due to a very small amount of excess oxygen in the reduced superconducting samples suggests that the T'-cuprates exhibiting the undoped superconductivity in the parent compounds are regarded as strongly correlated electron systems, as well as the hole-doped high-Tc cuprates. We show our proposed electronic structure model to understand the undoped superconductivity. Finally, unsolved future issues of the T'-cuprates are discussed.Comment: 13 pages, 8 figure

Muon-spin-relaxation and magnetic-susceptibility studies of effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13

Effects of the magnetic impurity Ni on the Cu-spin dynamics and superconductivity have been studied in La_2-x_Sr_x_Cu_1-y_Ni_y_O_4_ with x = 0.13 changing y finely up to 0.10. Compared with the case of the nonmagnetic impurity Zn, it has been found from the muon-spin-relaxation measurements that a large amount of Ni is required to stabilize a magnetic order of Cu spins. However, the evolution toward the stabilization of the magnetic order with increasing impurity concentration is qualitatively similar to each other. The area of the non-superconducting and slowly fluctuating or static region of Cu spins around Ni has been found to be smaller than that around Zn, suggesting that the pinning of rather long-ranged dynamical spin correlation such as the so-called dynamical stripe by Ni is weaker than that by Zn. This may be the reason why Zn destroys the superconductivity in the hole-doped high-T_c_ cuprates more markedly than Ni.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev.

Effect of the shape anisotropy on the magnetic configuration of (Ga,Mn)As and its evolution with temperature

We study the effect of the shape anisotropy on the magnetic domain configurations of a ferromagnetic semiconductor (Ga,Mn)As/GaAs(001) epitaxial wire as a function of temperature. Using magnetoresistance measurements, we deduce the magnetic configurations and estimate the relative strength of the shape anisotropy compared with the intrinsic anisotropies. Since the intrinsic anisotropy is found to show a stronger temperature dependence than the shape anisotropy, the effect of the shape anisotropy on the magnetic domain configuration is relatively enhanced with increasing temperature. This information about the shape anisotropy provides a practical means of designing nanostructured spin electronic devices using (Ga,Mn)As.Comment: 4 pages, 4 figures, to appear in J. Appl. Phy

Absence of the impurity-induced magnetic order in the electron-doped high-T_c_ cuprates Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4_

Zero-field muon-spin-relaxation measurements have been carried out in order to investigate the Zn- and Ni-substitution effects on the Cu-spin dynamics in the electron-doped Pr_0.86_LaCe_0.14_Cu_1-y_(Zn, Ni)_y_O_4+\alpa-\delta_ with y = 0, 0.01, 0.02, 0.05 and different values of the reduced oxygen content \delta(\delta \le 0.09). For the samples with y = 0 and very small \delta values of \delta < 0.01, a muon-spin precession due to the formation of a long-range antiferromagnetic order has been observed at low temperatures below \~ 5 K. For the moderately oxygen-reduced samples of 0.01 \le \delta \le 0.09, on the contrary, no muon-spin precession has been observed and the temperature dependence of the spectra is similar to one another regardless of the y value. That is, no impurity-induced slowing down of the Cu-spin fluctuations has been detected, which is very different from the results of the hole-doped high-T_c_ cuprates. The reason is discussed.Comment: 13 pages, 2 figures, Proceedings of ISS2004 (to be published in Physica C

Ambiguities of theoretical parameters and CP/T violation in neutrino factories

We study the optimal setup for observation of the CP asymmetry in neutrino factory experiments --- the baseline length, the muon energy and the analysis method. First, we point out that the statistical quantity which has been used in previous works doesn't represent the CP asymmetry. Then we propose the more suitable quantity, $\equiv \chi^{2}_{2}$, which is sensitive to the CP asymmetry. We investigate the behavior of $\chi^{2}_{2}$ with ambiguities of the theoretical parameters. The fake CP asymmetry due to the matter effect increases with the baseline length and hence the error in the estimation of the fake CP asymmetry grows with the baseline length due to the ambiguities of the theoretical parameters. Namely, we lose the sensitivity to the genuine CP-violation effect in longer baseline.Comment: 8pages, 2figures, Talk given by J. Sato at Joint U.S. / Japan Workshop on New Initiatives in Muon Lepton Flavor Violation and Neutrino Oscillation with High Intense Muon and Neutrino Sources, Honolulu, Hawaii, 2-6 Oct 200

Relation between shrinkage effect and compression of rotational spectrum in Λ7^7_\LambdaLi hypernucleus

It has been shown experimentally that the $^6$Li nucleus shrinks by adding a $\Lambda$ particle while its spectrum is also compressed. We discuss the compatibility of these two effects, contrasting also with a relation between the shrinkage effect and the stability of the spectrum in the $^9_\Lambda$Be hypernucleus. To this end, we employ two-body $d$-$^5_\Lambda$He and $\alpha$-$^5_\Lambda$He cluster models for the $^7_\Lambda$Li and $^9_\Lambda$Be hypernuclei, respectively. We first argue that a Gaussian-like interaction between two clusters leads to a stabilization of the spectrum against an addition of a $\Lambda$ particle, even though the intercluster distance is reduced. In the case of $^7_\Lambda$Li, the spin-orbit interaction between the intercluster motion and the deuteron spin has to be considered also. We show that the shrinkage effect makes the expectation value of the spin-orbit potential larger, lowering the excitation energy for the $^6$Li($3^+)\otimes \Lambda(1/2^+)$ level.Comment: 8 pages, 8 eps figure