arXiv subjects

S. Yamazaki

Publications and source records attributed to S. Yamazaki.

5 recordsLinked to original sources

arXiv2026

Isoscalar Giant Resonances in the even-A Pd Isotopes

Studies of the isoscalar giant monopole resonance (ISGMR) across the chart of nuclides provide insight into the incompressibility of nuclear matter near saturation density, K(infinity). Such studies had revealed a discrepancy between theoretical approaches: quasiparticle random phase approximation (QRPA) derived from Skyrme interactions reproduce the strength distributions of the ISGMR in the doubly-closed-shell nuclei 90Zr and 208Pb, but their descriptions of strength distributions in open-shell medium-heavy nuclei suggest higher centroid energies should be experimentally observed. The latter nuclei required a smaller K(infinity) and were thus deemed softer. The present work serves to add to this softness discourse by extracting ISGMR strength distributions for 104,106,108,110Pd via 386-MeV inelastic alpha-scattering. The extracted giant resonance strength distributions are consistent with expectations in this isotopic range. Additional Quasiparticle Vibration Coupling (QPVC) effects are included with the QRPA approach and compared to aforementioned ISGMR strength distributions.

nucl-ex↗

arXiv2015

The magnetic ground state properties of non-centrosymmetric CePt$_3$B$_{1-x}$Si$_x$

We present a study of the alloying series of the non-centrosymmetric $f$-electron intermetallic CePt$_3$B$_{1-x}$Si$_x$ by means of muon spin rotation and relaxation measurements. In addition, we include a high pressure magnetization investigation of the stoichiometric parent compound CePt$_3$B. From our data we establish the nature of the magnetic ground state properties of the series, derive the ordered magnetic moment as function of stoichiometry and gain insight into the evolution of the symmetry of the ordered magnetic state with $x$. We thus can verify the notion that the behavior of the sample series can essentially be understood within the framework of the Doniach phase diagram. Further, our findings raise the issue of the role the Dzyaloshinskii-Moriya magnetic interaction plays in correlated electron materials, and its effect on magnetic fluctuations in such materials.

cond-mat.str-el↗

arXiv2015

Electronic structure of Mott-insulator CaCu3Ti4O12: Photoemission and inverse photoemission study

We have performed the photoemission and inverse photoemission experiments to elucidate the origin of Mott insulating states in A-site ordered perovskite CaCu$_3$Ti$_4$O$_{12}$ (CCTO). Experimental results have revealed that Cu 3$d$-O 2$p$ hybridized bands, which are located around the Fermi level in the prediction of the local-density approximation (LDA) band calculations, are actually separated into the upper Hubbard band at $\sim$ 1.5 eV and the lower Hubbard band at $\sim$ $-$1.7 eV with a band gap of $\sim$ 1.5-1.8 eV. We also observed that Cu 3$d$ peak at $\sim$ $-$3.8 eV and Ti 3$d$ peak at $\sim$ 3.8 eV are further away from each other than as indicated in the LDA calculations. In addition, it is found that the multiplet strucutre around $-$9 eV includes a considerable number of O 2$p$ states. These observations indicate that the Cu 3$d$ and Ti 3$d$ electrons hybridized with the O 2$p$ states are strongly correlated, which originates in the Mott-insulating states of CCTO.

cond-mat.str-el↗

arXiv2011

Suzaku view of X-ray Spectral Variability of the Radio Galaxy Centaurus A : Partial Covering Absorber, Reflector, and Possible Jet Component

We observed a nearby radio galaxy, the Centaurus A (Cen A), three times with Suzaku in 2009, and measured the wide-band X-ray spectral variability more accurately than the previous measurements. The Cen A was in the active phase in 2009, and the flux became higher by a factor of 1.5--2.0 and the spectrum became harder than that in 2005. The Fe-K line intensity increased by 20--30% from 2005 to 2009. The correlation of the count rate between the XIS 3--8 keV and PIN 15--40 keV band showed a complex behavior with a deviation from a linear relation. The wide-band X-ray continuum in 2--200 keV can be fitted with an absorbed powerlaw model plus a reflection component, or a powerlaw with a partial covering Compton-thick absorption. The difference spectra between high and low flux periods in each observation were reproduced by a powerlaw with a partial covering Compton-thick absorption. Such a Compton-thick partial covering absorber was for the first time observed for the Cen A. The powerlaw photon index of the difference spectra in 2009 is almost the same as that of the time-averaged spectra in 2005, but steeper by $\sim0.2$ than that of the time-averaged spectra in 2009. This suggests an additional hard powerlaw component with a photon index of $<1.6$ in 2009. This hard component could be a lower part of the inverse-Compton-scattered component from the jet, whose gamma-ray emission has recently been detected with the Fermi/LAT.

astro-ph.HE↗

arXiv1999

Emission-Line Properties of MG2016+112: A Luminous Type-2 Quasar at High Redshift

We present new high signal-to-noise ratio spectra of the components B and C of the gravitational lensing system MG2016+112. We show that image C displays strong emission lines of Ly$α$, \NV, \CIV, \HeII, and \CIII redshifted to z=3.27, similar to images and B. We examine the emission-line flux ratios in order to put constraints on the lens models as well as to investigate the intrinsic nature of MG2016+112. The observed line ratios of B and C are consistent with those expected in the simple photo-ionization models for narrow-line region of active galactic nuclei (AGN) except for the enhanced \NV\ lines. The line ratios difference of components B and C can be interpreted as a difference in ionization parameters. This result is consistent with lens model prediction that C is a fold image of a slightly outer part of the nucleus. MG2016+112 is known to be very unique among the high-redshift AGN; it is neither an ordinary broad-line quasar nor a powerful radio galaxy as indicated by the width and flux ratio of the emission lines. Together with other observed properties discussed in literature, we argue that MG2016+112 is the highest redshift luminous radio-quiet type-2 quasar.

astro-ph↗