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387 results on '"Nagasawa, N."'

1. Low-Energy Optical Phonon Modes in the Caged Compound LaRu2Zn20

Author

Wakiya, K., Onimaru, T., Tsutsui, S., Matsumoto, K. T., Nagasawa, N., Baron, A. Q. R., Hasegawa, T., Ogita, N., Udagawa, M., and Takabatake, T.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science
Abstract

The caged compound LaRu2Zn20 exhibits a structural transition at TS =150 K, whose driving mechanism remains elusive. We have investigated atomic dynamics by the measurements of specific heat C and inelastic X-ray scattering (IXS). The lattice part of the specific heat Clat divided by T3, Clat/T3, shows a broad peak at around 15 K, which is reproduced by two Einstein modes with characteristic temperatures of 35 K and 82 K, respectively. IXS measurements along the [111] and [110] directions reveal optical phonon modes at 3 meV (35 K) and 7 meV (80 K), respectively, whose values agree with the values of Einstein temperatures. The first principles calculation has assigned the phonon modes at 3 meV as the optical modes of Zn atoms located at the middle of two La atoms. The low-energy vibration of the Zn atom perpendicular to the there-fold axis is thought to lead the structural instability of LaRu2Zn20., Comment: 11pages, 4 figures

Published
2014
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2. Simultaneous Superconducting and Antiferroquadrupolar Transitions in PrRh$_{2}$Zn$_{20}$

Author

Onimaru, T., Nagasawa, N., Matsumoto, K. T., Wakiya, K., Umeo, K., Kittaka, S., Sakakibara, T., Matsushita, Y., and Takabatake, T.

Subjects
Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Condensed Matter - Superconductivity
Abstract

Superconducting and antiferroquadrupolar (AFQ) transitions in a Pr-based compound PrRh2Zn20 have been found to occur simultaneously at Tc=TQ=0.06 K. The superconducting transition manifests itself by zero resistance and large diamagnetic susceptibility. The specific heat exhibits a Schottky anomaly peaking at 14 K and magnetization curves measured at 2 K show anisotropic behaviors. The analysis of these data indicates that the crystalline electric field (CEF) ground state of the trivalent Pr ion is the non-Kramers Gamma3 doublet with the quadrupolar degrees of freedom. A sharp peak in the specific heat at 0.06 K has been attributed not to the superconducting transition but to the AFQ transition because the ordering temperature TQ decreases in B || [100] but increases in B || [110] and B || [111] with increasing B up to 6 T. This anisotropic behavior of TQ(B) can be well explained by a two-sublattice mean-field calculation, which corroborates the AFQ ordered state below TQ. The entropy release at TQ is only 10% of Rln2 expected for the Gamma3 doublet, suggesting possible interplay between the quadrupolar degrees of freedom and the superconductivity., Comment: 18 page, 6 figures, accepted for publication in Phys. Rev. B

Published
2012
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3. Bosonic stimulation of cold 1s excitons into a harmonic potential minimum in Cu$_2$O

Author

Naka, N. and Nagasawa, N.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Statistical Mechanics
Abstract

Density distribution of cold exciton clouds generated into a strain-induced potential well by two-photon excitation in Cu$_2$O is studied at 2 K. We find that an anomalous spike, which can be interpreted as accumulation of the excitons into the ground state, emerges at the potential minimum. The accumulation can be due to stimulated scattering of cold excitons, mediated by acoustic phonon emission. Possibility of the formation of the thermodynamic Bose-Einstein condensate of paraexcitons has been discussed., Comment: Submitted to Solid State Communications on 17 December, 2002

Published
2003
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4. Vacuum Tltraviolet Search from Thorium-229 Isomer in Crystal Toward Solid-State Nuclear Clock

Author

Takatori, S., primary, Fukunaga, Y., additional, Guan, M., additional, Hiraki, T., additional, Masuda, T., additional, Ogake, R., additional, Okai, K., additional, Sasao, N., additional, Shimizu, K., additional, Uetake, S., additional, Yoshimi, A., additional, Yoshimura, K., additional, Yoshimura, M., additional, Tamasaku, K., additional, Kasamatsu, Y., additional, Yasuda, Y., additional, Beeks, K., additional, Schaden, F., additional, Schumm, T., additional, Kitao, S., additional, Seto, M., additional, Fujimoto, H., additional, Watanabe, T., additional, Konashi, K., additional, Watanabe, M., additional, Haba, H., additional, Shigekawa, Y., additional, Yamaguchi, A., additional, Nagasawa, N., additional, and Yoda, Y., additional

Published
2023
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23. Structural Evolution of Deformed Polyethylene Studied with Positron.

Author

Kobayashi, Y., Yamawaki, M., Oka, T., Sato, K., Uesugi, N., Hattori, K., Nagasawa, N., and Washio, M.

Subjects
HIGH density polyethylene, LOW density polyethylene, POSITRON annihilation, POLYETHYLENE, POSITRONS, MOLECULAR weights
Abstract

Uniaxially stretched high density polyethylene (HDPE), low density polyethylene (LDPE) and ultra-high molecular weight polyethylene (UHMWPE) were studied by positron annihilation lifetime spectroscopy (PALS). The pick-off annihilation lifetime of ortho-positronium (o-Ps) was progressively shortened by stretching. This shortening is due to development of anisotropy in sub-nm size open space (free volume) for o-Ps localization. Simple analysis by an extended Tao-Eldrup model suggests that the hole anisotropy is much less than the bulk anisotropy possibly due to structural relaxation. Correlation between the o-Ps relative intensity and lifetime points to one-stage deformation of LDPE and UHMWPE, and multiple-stage deformation of HDPE, respectively. A recently commercialized positron lifetime spectrometer, which permits PALS to be performed with a single specimen, was found to be applicable to stretched polymers. [ABSTRACT FROM AUTHOR]

Published
2019
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24. Structural Evolution in Deformed Polyethylene Studied with Positrons

Author

Y.Kobayashi, Yamawaki, M., Oka, T., Sato, K., Uesugi, N., Hattori, K., Nagasawa, N., and Washio, M.

Abstract

Different kinds of polyethylene were subjected to uniaxial deformation and their structural evolution was investigated by positron annihilation lifetime spectroscopy (PALS) and coincident Doppler broadening spectroscopy (CDB). The pick-off annihilation lifetime of ortho-positronium (o-Ps) was progressively shortened by deformation, possibly due to anisotropic elongation of the free volume and enhanced overlap of the o-Ps wavefunction with the surrounding polyethylene molecules. The anisotropy elongation of the free volume in deformed polyethylene was also implied by CDB. The intensity of o-Ps was enhanced in high density polyethylene (HDPE) and ultra-high-molecular-weight polyethylene (UHMWPE) by deformation, but not in low density polyethylene (LDPE). This suggests that the destruction of crystallites may play a significant role in the deformation of HDPE and UHMWPE but not in LDPE. Comparison of the PALS data, obtained with two specimens sandwiching the positron source, with those obtained with a single specimen by using a commercial PALS system recently developed by Yamawaki et al confirmed the usefulness of the commercial PALS system in the study of deformed polymers., 18th International Conference on Positron Annihilation(ICPA2018)

Published
2018

34. Anomalous Enhancement of Seebeck Coefficient in Pr-Based 1-2-20 System with Non-Kramers Doublet Ground States

Author

Machida, Y, primary, Yoshida, T, additional, Ikeura, T, additional, Izawa, K, additional, Nakama, A, additional, Higashinaka, R, additional, Aoki, Y, additional, Sato, H, additional, Sakai, A, additional, Nakatsuji, S, additional, Nagasawa, N, additional, Matsumoto, K, additional, Onimaru, T, additional, and Takabatake, T, additional

Published
2015
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44. Radiolysis studies of aqueous κ-carrageenan

Author

Abad, L.V., primary, Kudo, H., additional, Saiki, S., additional, Nagasawa, N., additional, Tamada, M., additional, Fu, H., additional, Muroya, Y., additional, Lin, M., additional, Katsumura, Y., additional, Relleve, L.S., additional, Aranilla, C.T., additional, and DeLaRosa, A.M., additional

Published
2010
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