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Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:140 Percentile:99.81(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Journal Articles

Active sites and mechanisms for oxygen reduction reaction on nitrogen-doped carbon alloy catalysts; Stone-Wales defect and curvature effect

Chai, G.-L.*; Hou, Z.*; Shu, D.-J.*; Ikeda, Takashi; Terakura, Kiyoyuki*

Journal of the American Chemical Society, 136(39), p.13629 - 13640, 2014/10

 Times Cited Count:198 Percentile:97.69(Chemistry, Multidisciplinary)

Carbon alloy catalysts (CACs) are promising catalysts for oxygen reduction reaction (ORR) to substitute Pt. However, despite extensive studies on CACs the reaction sites and mechanisms for ORR are still in controversy. Herein, we present rather general consideration on possible ORR mechanisms for various structures in nitrogen doped CACs based on the first principles calculations. Our study indicates that only a particular structure of a nitrogen pair doped Stone-Wales defect provides a good active site. The ORR activity of this structure can be tuned by the curvature around the active site, which makes its limiting potential approaching the maximum limiting potential (0.80 V) in the volcano plot for the ORR activity of CACs. The calculated results can be compared with the recent experimental ones of the half wave potential for CAC systems that range from 0.60 V to 0.80 V in the reversible-hydrogen-electrode scale.

Journal Articles

Interplay between oxidized monovacancy and nitrogen doping in graphene

Hou, Z.*; Shu, D.-J.*; Chai, G.-L.*; Ikeda, Takashi; Terakura, Kiyoyuki*

Journal of Physical Chemistry C, 118(34), p.19795 - 19805, 2014/08

 Times Cited Count:10 Percentile:38.87(Chemistry, Physical)

In most of the N-doped graphene which attracts strong attention in the context of precious-metal free catalysts and nanoelectronics, the oxygen content is generally higher than or at least comparable to the nitrogen content. We perform density functional theory calculations to study the interplay of oxidized monovacancies and the nitrogen doping, motivated by the fact that MV is more frequently observed and more chemically active than divacancy and Stone-Wales defect. We determine the phase diagrams of un-doped and nitrogen-doped oxidized MVs as a function of temperature and partial pressure of O$$_{2}$$ and H$$_{2}$$ gases. The modification of the electronic structure of MV by oxidation and N doping is studied. Our results show that the ether group is a common component in stable configurations of oxidized MVs. Most of the stable configurations of oxidized MVs do not induce any carriers.

Journal Articles

Suppression of time-reversal symmetry breaking superconductivity in Pr(Os$$_{1-x}$$Ru$$_x$$)$$_4$$Sb$$_{12}$$ and Pr$$_{1-y}$$La$$_y$$Os$$_4$$Sb$$_{12}$$

Shu, L.*; Higemoto, Wataru; Aoki, Yuji*; Hillier, A. D.*; Oishi, Kazuki*; Ishida, Kenji*; Kadono, Ryosuke*; Koda, Akihiro*; Bernal, O. O.*; MacLaughlin, D. E.*; et al.

Physical Review B, 83(10), p.100504_1 - 100504_4, 2011/03

 Times Cited Count:28 Percentile:75.21(Materials Science, Multidisciplinary)

Zero-field muon spin relaxation experiments have been carried out in the Pr(Os$$_{1-x}$$Ru$$_x$$)$$_4$$Sb$$_{12}$$ and Pr$$_{1-y}$$La$$_y$$Os$$_4$$Sb$$_{12}$$ alloy systems to investigate broken time-reversal symmetry (TRS) in the superconducting state, signaled by the onset of a spontaneous static local magnetic field B$$_s$$. In both alloy series B$$_s$$ initially decreases linearly with solute concentration. Ru doping is considerably more efficient than La doping, with a 50% faster initial decrease. The data suggest that broken TRS is suppressed for Ru concentration $$xgeq$$0.6 but persists for essentially all La concentrations. Our data support a crystal-field excitonic cooper pairing mechanism for TRS-breaking superconductivity.

Journal Articles

Novel features in filled skutterudites containing rare-earth elements with a plural number of 4f-electrons

Sato, Hideyuki*; Aoki, Yuji*; Kikuchi, Daisuke*; Sugawara, Hitoshi*; Higemoto, Wataru; Oishi, Kazuki; Ito, Takashi; Heffner, R. H.; Saha, S. R.*; Koda, Akihiro*; et al.

Physica B; Condensed Matter, 404(5-7), p.749 - 753, 2009/04

 Times Cited Count:4 Percentile:22.79(Physics, Condensed Matter)

Wide varieties of strongly correlated electron phenomena are performed on the stage of a filled skutterudite structure. Especially when one of the players contains a plural number of 4f electrons, the orbital degrees of freedom play a major role as a new type of nonmagnetic and/or weak-magnetic phenomena. Several examples found in Pr- and Sm-based filled skutterudites are introduced in relation to muon spin relaxation experiments.

Journal Articles

Influence of self-irradiation on the magnitude of the superfluid density in PuCoGa$$_5$$ probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Ito, Takashi; Higemoto, Wataru; Morris, G. D.*; Bauer, E. D.*; Graf, M. J.*; Zhu, J.-X.*; Morales, L. A.*; Sarrao, J. L.*; et al.

Physica B; Condensed Matter, 403(5-9), p.1013 - 1014, 2008/04

 Times Cited Count:0 Percentile:0(Physics, Condensed Matter)

PuCoGa$$_5$$ has attracted much interest because it is the first Pu-based superconductor, having an order of magnitude higher transition temperature $$T_{rm c}=18.5$$K than the isostructural heavy fermion superconductor CeCoIn$$_5$$ ($$T_{rm c}=2.3$$K). The mechanism of the superconductivity in PuCoGa$$_5$$ is still under investigation, though recent experiments and theory suggest a magnetic origin. A unique aspect of this compound is the self-irradiation damage because Pu ($$^{239}$$Pu, $$T^{1/2}$$ = 24,000 years) creates lattice defects which scatter electrons and, hence, break superconducting pairs. In order to elucidate the magnitude and temperature dependence of the magnetic penetration depth $$lambda$$, we have performed $$mu$$SR measurements in the same PuCoGa$$_5$$ single crystals after 25 and 400 days of aging. We found that $$T_{rm c}$$ decreased from 18.5K to 15K for the aged sample, yet a quasi-linear temperature dependence was found for the low-temperature $$lambda(T)$$ in both the fresh and aged sample, consistent with $$d$$-wave pairing symmetry. The magnitude of the muon spin relaxation rate $$sigma$$ in the aged sample, $$sigmapropto 1/lambda^2proptorho_s/m^*$$, where $$rho_s$$ and $$m^*$$ are the superfluid density and the effective mass, respectively, is reduced by about 70% compared to fresh sample. This indicates that the scattering from self-irradiation induced defects is not in the limit of the conventional Abrikosov-Gor'kov pair-breaking theory, but rather in the limit of short coherence length (about 2nm in PuCoGa$$_5$$) superconductivity.

Journal Articles

$$mu$$SR study of the effects of Ce dilution on the development of the heavy-fermion state in (Ce,La)$$_2$$IrIn$$_8$$

Oishi, Kazuki; Heffner, R. H.; Ito, Takashi; Higemoto, Wataru; Morris, G. D.*; Hur, N.*; Bauer, E. D.*; Sarrao, J. L.*; Thompson, J. D.*; MacLaughlin, D. E.*; et al.

Journal of Physics and Chemistry of Solids, 68(11), p.2068 - 2071, 2007/11

 Times Cited Count:2 Percentile:13.7(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

The Search for magnetic order in $$delta$$-Pu metal using muon spin relaxation

Heffner, R. H.; Oishi, Kazuki; Fluss, M. J.*; Morris, G. D.*; MacLaughlin, D. E.*; Shu, L.*; Chung, B. W.*; McCall, S. K.*; Bauer, E. D.*; Sarrao, J. L.*; et al.

Journal of Alloys and Compounds, 444-445, p.80 - 83, 2007/10

 Times Cited Count:8 Percentile:51.29(Chemistry, Physical)

We summarize the results of muon spin relaxation ($$mu$$SR) measurements carried out in$$alpha$$- and $$delta$$-Pu and in the superconducting state ofPuCoGa$$_5$$. In Pu metal, interest has centered on whether or not magnetic order exists in the hightemperature fcc $$delta$$ phase,The Pu metal studies were designed to search for evidence of magnetic ordering, andhave set the most stringent limits to date for the ordered moment. In PuCoGa$$_5$$ the temperature dependence of themagnetic penetration depth $$lambda$$(T) was investigated in a fresh sample and again in the same sampleafter 400 days of aging. We find $$lambda$$(T)$$propto$$ T for T $$<$$ Tc/2, indicating a line of nodes in thesuperconducting order parameter. Remarkably, the temperature dependence of $$lambda$$(T) is littlechanged even after significant radiation damage.

Journal Articles

Muon spin rotation measurements of the superfluid density in fresh and aged superconducting PuCoGa$$_5$$

Oishi, Kazuki; Heffner, R. H.; Morris, G. D.*; Bauer, E. D.*; Graf, M. J.*; Zhu, J.-X.*; Morales, L. A.*; Sarrao, J. L.*; Fluss, M. J.*; MacLaughlin, D. E.*; et al.

Physical Review B, 76(6), p.064504_1 - 064504_10, 2007/08

 Times Cited Count:13 Percentile:53.86(Materials Science, Multidisciplinary)

Journal Articles

Muon spin relaxation and hyperfine-enhanced $$^{141}$$Pr nuclear spin dynamics in Pr(Os,Ru)$$_4$$Sb$$_{12}$$ and (Pr,La)Os$$_4$$Sb$$_{12}$$

Shu, L.*; MacLaughlin, D. E.*; Aoki, Yuji*; Tsunashima, Yoshino*; Yonezawa, Yuki*; Sanada, Shotaro*; Kikuchi, Daisuke*; Sato, Hideyuki*; Heffner, R. H.; Higemoto, Wataru; et al.

Physical Review B, 76(1), p.014527_1 - 014527_8, 2007/07

 Times Cited Count:20 Percentile:65.43(Materials Science, Multidisciplinary)

Journal Articles

Magnetic penetration depth and self-induced irradiation effects in superconducting PuCoGa$$_5$$ probed by muon spin rotation

Oishi, Kazuki; Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Bauer, E. D.*; Morales, L. A.*; Sarrao, J. L.*; MacLaughlin, D. E.*; Shu, L.*; Ito, Takashi; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.566 - 568, 2007/03

no abstracts in English

Journal Articles

Time reversal symmetry breaking in superconducting (Pr,La)Os$$_4$$Sb$$_{12}$$ and Pr(Os,Ru)$$_4$$Sb$$_{12}$$

Shu, L.*; Higemoto, Wataru; Aoki, Yuji*; Frederick, N. A.*; Yuhasz, W. M.*; Heffner, R. H.; Oishi, Kazuki; Ishida, Kenji*; Kadono, Ryosuke*; Koda, Akihiro*; et al.

Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.551 - 553, 2006/11

Journal Articles

$$mu$$SR studies of Pu metal and the Pu-based superconductor PuCoGa$$_5$$

Heffner, R. H.; Bauer, E. D.*; Chung, B.*; Fluss, M. J.*; Higemoto, Wataru; Ito, Takashi; MacLaughlin, D. E.*; Morales, L. A.*; Morris, G. D.*; Oishi, Kazuki; et al.

Journal of the Physical Society of Japan, 75(Suppl.), p.14 - 19, 2006/08

no abstracts in English

Journal Articles

New limits on the ordered moments in $$alpha$$-Pu and Ga-stabilized $$delta$$-Pu

Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Chung, B.*; MacLaughlin, D. E.*; Shu, L.*; Anderson, J. E.*

Physica B; Condensed Matter, 374-375, p.163 - 166, 2006/03

 Times Cited Count:8 Percentile:40.24(Physics, Condensed Matter)

The $$mu$$SR measurements in pulutonium metals are reported for the first time. The ground-state properties of Pu metal is not understood clearly. We found the upper limits of the ordered moment in $$alpha$$-Pu and $$delta$$-stabilized Pu is $$<10^{-3}mu_B$$ at $$sim$$4K.

Journal Articles

$$mu$$SR studies of the superconducting order parameter in PuCoGa$$_5$$

Morris, G. D.*; Heffner, R. H.; Bauer, E. D.*; Morales, L. A.*; Sarrao, J. L.*; Fluss, M. J.*; MacLaughlin, D. E.*; Shu, L.*; Anderson, J. E.*

Physica B; Condensed Matter, 374-375, p.180 - 183, 2006/03

 Times Cited Count:15 Percentile:58.07(Physics, Condensed Matter)

Journal Articles

Evolution of the heavy fermion state in Ce$$_2$$IrIn$$_8$$

Heffner, R. H.; Morris, G. D.*; Bauer, E. D.*; Sarrao, J. L.*; Thompson, J. D.*; MacLaughlin, D. E.*; Shu, L.*

Physica B; Condensed Matter, 375-375, p.184 - 187, 2006/03

 Times Cited Count:6 Percentile:32.73(Physics, Condensed Matter)

Journal Articles

Critical slowing down in the geometrically frustrated pyrochlore antiferromagnet Gd$$_2$$Ti$$_2$$O$$_7$$

MacLaughlin, D. E.*; Rose, M. S.*; Anderson, J. E.*; Shu, L.*; Heffner, R. H.; Kimura, Tsuyoshi*; Morris, G. D.*; Bernal, O. O.*

Physica B; Condensed Matter, 374-375, p.142 - 144, 2006/03

 Times Cited Count:3 Percentile:18.82(Physics, Condensed Matter)

Longitudinal-field muon spin relaxation experiments have been carried out in the paramagnetic state of single-crystal Gd$$_2$$Ti$$_2$$O$$_7$$ just above the phase transition. At high applied fields the relaxation time is proportional to field. At low fields the relaxation rate increases markedly as the freezing temperature is approached. This behavior is consistent with the very long autocorrelation function cutoff time.

Journal Articles

Limits for ordered magnetism in Pu from muon spin rotation spectroscopy

Heffner, R. H.; Morris, G. D.*; Fluss, M. J.*; Chung, B.*; McCall, S.*; MacLaughlin, D. E.*; Shu, L.*; Oishi, Kazuki; Bauer, E. D.*; Sarrao, J. L.*; et al.

Physical Review B, 73(9), p.094453_1 - 094453_5, 2006/03

 Times Cited Count:33 Percentile:78.73(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Spin freezing and non-glassy dynamics in Ce$$_{0.2}$$La$$_{0.8}$$RhIn$$_5$$

MacLaughlin, D. E.*; Shu, L.*; Anderson, J. E.*; Heffner, R. H.; Morris, G. D.*; Bernal, O. O.*; Kim, J. S.*; Stewart, G. R.*

Physica B; Condensed Matter, 378-380, p.144 - 145, 2006/02

 Times Cited Count:0 Percentile:0(Physics, Condensed Matter)

Journal Articles

Penetration depth study in the heavy-fermion superconductor PrOs$$_4$$Sb$$_{12}$$

Shu, L.*; MacLaughlin, D. E.*; Heffner, R. H.; Callaghan, F. D.*; Sonier, J. E.*; Morris, G. D.*; Bernal, O. O.*; Bosse, A.*; Anderson, J. E.*; Yuhasz, W. M.*; et al.

Physica B; Condensed Matter, 374-375, p.247 - 250, 2006/01

 Times Cited Count:6 Percentile:32.73(Physics, Condensed Matter)

27 (Records 1-20 displayed on this page)