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論文

Quantum critical behavior of the hyperkagome magnet MnCoSi

山内宏樹; Sari, D. P.*; 安井幸夫*; 坂倉輝俊*; 木村宏之*; 中尾朗子*; 大原高志; 本田孝志*; 樹神克明; 井川直樹; et al.

Physical Review Research (Internet), 6(1), p.013144_1 - 013144_9, 2024/02

https://doi.org/10.1103/PhysRevResearch.6.013144

-Mn-type family alloys Mn have three-dimensional antiferromagnetic (AFM) corner-shared triangular network. The antiferromagnet MnRhSi shows magnetic short-range order (SRO) over a wide temperature range of approximately 500 K above the Nel temperature $T_{rm N}$ = 190 K. MnCoSi has the smallest lattice parameter and the lowest $T_{rm N}$ in the family compounds. The quantum critical point (QCP) from AFM to the quantum paramagnetic state is expected near a cubic lattice parameter of 6.15 of MnCoSi is only 140 K, quantum critical behavior is observed in MnCoSi as the enhancement of the electronic specific heat coefficient . We study how the magnetic SRO appears in MnCoSi by using neutron scattering, SR, and physical property measurements. The experimental results show that the neutron scattering intensity of the magnetic SRO does not change much regardless of the suppressed magnetic moment in the long-range magnetic ordered state compared to those of MnRhSi. The initial asymmetry drop ratio of SR above $T_{rm N}$ becomes small, and the magnetic SRO temperature $T_{SRO}$ is suppressed to 240 K. The results suggest that the MnCoSi is close to the QCP in the Mn system.

論文

第1回日本保健物理学会・日本放射線安全管理学会合同シンポジウム印象記

山田椋平*; 玉熊佑紀*; 桑田遥*; 三枝裕美*; 渡邊裕貴; 廣田誠子*; Jin, Q.*; Cai, Y.*

保健物理(インターネット), 58(3), p.169 - 177, 2023/11

https://doi.org/10.5453/jhps.58.169

本報告は、2023年6月29日と30日の2日間にわたり開催された第1回日本保健物理学会・日本放射線安全管理学会合同シンポジウム(オンライン)の概要について報告するものである。

論文

Multiple mechanisms in proton-induced nucleon removal at 100 MeV/nucleon

Pohl, T.*; Sun, Y. L.*; Obertelli, A.*; Lee, J.*; Gmez-Ramos, M.*; 緒方一介*; 吉田数貴; Cai, B. S.*; Yuan, C. X.*; Brown, B. A.*; et al.

Physical Review Letters, 130(17), p.172501_1 - 172501_8, 2023/04

https://doi.org/10.1103/PhysRevLett.130.172501

被引用回数：7 パーセンタイル：87.40(Physics, Multidisciplinary)

大きなフェルミ面非対称性を持つ陽子過剰な $^{14}$ O原子核からの100MeV/nucleonでの陽子による陽子・中性子除去反応について報告した。この結果は、quasi-freeノックアウト反応、非弾性散乱、核子移行反応を含む複数の反応機構の定量的寄与を初めて示すものである。このようなエネルギー領域では通常無視される非弾性散乱と核子移行の寄与が、弱束縛陽子と強束縛中性子の除去反応断面積にそれぞれ約50%と30%寄与していることが示された。

論文

Two-step Mott transition in Ni(S,Se); SR studies and charge-spin percolation model

Sheng, Q.*; 金子竜也*; Yamakawa, Kohtaro*; Guguchia, Z.*; Gong, Z.*; Zhao, G.*; Dai, G.*; Jin, C.*; Guo, S.*; Fu, L.*; et al.

Physical Review Research (Internet), 4(3), p.033172_1 - 033172_14, 2022/09

https://doi.org/10.1103/PhysRevResearch.4.033172

A pyrite system NiS $_{2-x}$ Se exhibits a bandwidth controlled Mott transition via (S,Se) substitutions in a two-step process: the antiferromagnetic insulator (AFI) to antiferromagnetic metal (AFM) transition at 0.45 followed by the AFM to paramagnetic metal (PMM) transition at 1.0. Among a few other Mott systems which exhibit similar two-step transitions, Ni(S,Se) is of particular interest because a large intermediate AFM region in the phase diagram would provide unique opportunities to study the interplay between the spin and charge order. By comparing and combining our muon spin relaxation studies and previous neutron scattering studies, here we propose a picture where the spin order is maintained by the percolation of "nonmetallic" localized and dangling Ni moments surrounded by S, while the charge transition from AFI to AFM is caused by the percolation of the conducting paths generated by the Ni-Se-Ni bonds.

論文

Neutron spectroscopy evidence on the dual nature of magnetic excitations in a van der Waals metallic ferromagnet Fe $_{2.75}$ GeTe $_{2}$

Bao, S.*; Wang, W.*; Shangguan, Y.*; Cai, Z.*; Dong, Z.-Y.*; Huang, Z.*; Si, W.*; Ma, Z.*; 梶本亮一; 池内和彦*; et al.

Physical Review X, 12(1), p.011022_1 - 011022_15, 2022/02

https://doi.org/10.1103/PhysRevX.12.011022

被引用回数：25 パーセンタイル：94.45(Physics, Multidisciplinary)

In the local or itinerant extreme, magnetic excitations can be described by the Heisenberg model which treats electron spins as localized moments, or by the itinerant-electron model where the exchange interaction between electrons leads to unequal numbers of electrons with up and down spins. However, the nature of the magnetic excitations has been elusive when both local moments and itinerant electrons are present in the intermediate range. Using inelastic neutron scattering, we provide direct spectroscopic evidence on the coexistence of and interplay between local moments and itinerant electrons in a van der Waals metallic ferromagnet Fe $_{2.72}$ GeTe $_{2}$ , which can sustain tunable room-temperature ferromagnetism down to the monolayer limit. We find that there exist ferromagnetic spin-wave excitations dispersing from the zone center at low energies resulting from local moments and a columnlike broad continuum at the zone boundary at high energies up to over 100 meV resulting from itinerant electrons. Unlike the two-dimensional crystal structure, the low-energy mode exhibits a three-dimensional nature, and the high-energy mode also has an out-of-plane dependence. Both modes persist well above the Curie temperature of 160 K. Our neutron spectroscopic data reveal that the low-energy spin waves at 100 K are more coherent than those at 4 K, which is evidence of the weakening of the Kondo screening at high temperatures. These results unambiguously demonstrate the coexistence of local moments and itinerant electrons and the Kondo effect between these two components in Fe $_{2.72}$ GeTe $_{2}$ . Such behaviors are generally expected in heavy-fermion systems with heavy electrons but are rarely clearly observed in materials with light electrons. These findings shed light on the understanding of magnetism in transition-metal compounds.

論文

Evidence for strong correlations at finite temperatures in the dimerized magnet Na $_{2}$ Cu $_{2}$ TeO $_{6}$

Shangguan, Y.*; Bao, S.*; Dong, Z.-Y.*; Cai, Z.*; Wang, W.*; Huang, Z.*; Ma, Z.*; Liao, J.*; Zhao, X.*; 梶本亮一; et al.

Physical Review B, 104(22), p.224430_1 - 224430_8, 2021/12

https://doi.org/10.1103/PhysRevB.104.224430

被引用回数：1 パーセンタイル：5.86(Materials Science, Multidisciplinary)

Dimerized magnets forming alternating Heisenberg chains exhibit quantum coherence and entanglement and thus can find potential applications in quantum information and computation. However, magnetic systems typically undergo thermal decoherence at finite temperatures. Here, we show inelastic neutron scattering results on an alternating antiferromagnetic-ferromagnetic chain compound Na $_{2}$ Cu $_{2}$ TeO $_{6}$ that the excited quasiparticles can counter thermal decoherence and maintain strong correlations at elevated temperatures. At low temperatures, we observe clear dispersive singlet-triplet excitations arising from the dimers formed along the crystalline -axis. The excitation gap is of 18 meV and the bandwidth is about half of the gap. The band top energy has a weak modulation along the [100] direction, indicative of a small interchain coupling. The gap increases while the bandwidth decreases with increasing temperature, leading to a strong reduction in the available phase space for the triplons. As a result, the Lorentzian-type energy broadening becomes highly asymmetric as the temperature is raised. These results are associated with a strongly correlated state resulting from hard-core constraint and quasiparticle interactions. We consider these results to be not only evidence for strong correlations at finite temperatures in Na $_{2}$ Cu $_{2}$ TeO $_{6}$ , but also for the universality of the strongly correlated state in a broad range of quantum magnetic systems.

論文

Half-integer Shapiro steps in strong ferromagnetic Josephson junctions

Yao, Y.*; Cai, R.*; Yang, S.-H.*; Xing, W.*; Ma, Y.*; 森道康; Ji, Y.*; 前川禎通; Xie, X.-C.*; Han, W.*

Physical Review B, 104(10), p.104414_1 - 104414_6, 2021/09

https://doi.org/10.1103/PhysRevB.104.104414

被引用回数：7 パーセンタイル：36.41(Materials Science, Multidisciplinary)

We report the experimental observation of half-integer Shapiro steps in the strong ferromagnetic Josephson junction (Nb-NiFe-Nb) by investigating the current-phase relation under radio-frequency microwave excitation. The half-integer Shapiro steps are robust in a wide temperature range from T = 4 to 7 K. The half-integer Shapiro steps could be attributed to co-existence of 0- and -states in the strong ferromagnetic NiFe Josephson junctions with the spatial variation of the NiFe thickness. This scenario is also supported by the high-resolution transmission electron microscopy characterization of the Nb/NiFe/Nb junction.

論文

Enhancement of fatigue resistance by overload-induced deformation twinning in a CoCrFeMnNi high-entropy alloy

Lam, T.-N.*; Lee, S. Y.*; Tsou, N.-T.*; Chou, H.-S.*; Lai, B.-H.*; Chang, Y.-J.*; Feng, R.*; 川崎卓郎; Harjo, S.; Liaw, P. K.*; et al.

Acta Materialia, 201, p.412 - 424, 2020/12

https://doi.org/10.1016/j.actamat.2020.10.016

被引用回数：40 パーセンタイル：91.75(Materials Science, Multidisciplinary)

We examined fatigue-crack-growth behaviors of CoCrFeMnNi high-entropy alloys (HEAs) under as-fatigued and tensile-overloaded conditions using neutron-diffraction measurements coupled with diffraction peak-profile analyses. We applied both high-resolution transmission electron microscopy (HRTEM) and neutron-diffraction strain mapping for the complementary microstructure examinations. Immediately after a single tensile overload, the crack-growth-retardation period was obtained by enhancing the fatigue resistance, as compared to the as-fatigued condition. The combined mechanisms of the overload-induced larger plastic deformation, the enlarged compressive residual stresses and plastic-zone size, the crack-tip blunting ahead of the crack tip, and deformation twinning governed the pronounced macroscopic crack-growth-retardation behavior following the tensile overload.

論文

Evidence for magnon-phonon coupling in the topological magnet Cu $_{3}$ TeO $_{6}$

Bao, S.*; Cai, Z.*; Si, W.*; Wang, W.*; Wang, X.*; Shangguan, Y.*; Ma, Z.*; Dong, Z.-Y.*; 梶本亮一; 池内和彦*; et al.

Physical Review B, 101(21), p.214419_1 - 214419_8, 2020/06

https://doi.org/10.1103/PhysRevB.101.214419

被引用回数：20 パーセンタイル：73.24(Materials Science, Multidisciplinary)

We perform thermodynamic and inelastic neutron scattering (INS) measurements to study the lattice dynamics (phonons) of a cubic collinear antiferromagnet Cu $_{3}$ TeO $_{6}$ which hosts topological spin excitations (magnons). While the specific heat and thermal conductivity results show that the thermal transport is dominated by phonons, the deviation of the thermal conductivity from a pure phononic model indicates that there is a strong coupling between magnons and phonons. In the INS measurements, we find a mode in the excitation spectra at 4.5 K, which exhibits a slight downward dispersion around the Brillouin zone center. This mode disappears above the Nel temperature and thus cannot be a phonon. Furthermore, the dispersion is distinct from that of a magnon. Instead, it can be explained by the magnon-polaron mode, collective excitations resulting from the hybridization between magnons and phonons. We consider the suppression of the thermal conductivity and emergence of the magnon-polaron mode to be evidence for magnon-phonon coupling in Cu $_{3}$ TeO $_{6}$ .

論文

Spin dynamics of a magnetic Weyl semimetal Sr $_{1-x}$ Mn $_{1-y}$ Sb $_{2}$

Cai, Z.*; Bao, S.*; Wang, W.*; Ma, Z.*; Dong, Z.-Y.*; Shangguan, Y.*; Wang, J.*; Ran, K.*; Li, S.*; 蒲沢和也*; et al.

Physical Review B, 101(13), p.134408_1 - 134408_10, 2020/04

AA2020-0050.pdf:5.09MB

https://doi.org/10.1103/PhysRevB.101.134408

被引用回数：6 パーセンタイル：33.94(Materials Science, Multidisciplinary)

ディラック物質は量子現象と共にキャリアの役割を探索するのに良い系で、磁気ワイル半金属のSr $_{1-x}$ Mn $_{1-y}$ Sb $_{2}$ はワイルフェルミオンとマグノンの関係を研究する良い舞台である。本研究では、Sr $_{1-x}$ Mn $_{1-y}$ Sb $_{2}$ の単結晶の中性子非弾性散乱実験を行い、磁性Mn層の分散は約76meVまで広がり、層間の分散は6meVの狭いバンド幅を持つことを見出した。また、これらの実験結果はハイゼンベルグ・スピンハミルトニアンを用いた線形スピン波理論によって再現可能である。本研究では、ワイルフェルミオンとマグノンが共存しているにもかかわらず、Sr $_{1-x}$ Mn $_{1-y}$ Sb $_{2}$ 中のワイルフェルミオンが磁気ダイナミクスに影響を与えているという明確な証拠は得られなかった。これは、ワイルフェルミオンとマグノンがSb層とMn層に別々に存在し、この擬二次元性による層間結合の弱さに起因するもの考えられる。

論文

Evidence for singular-phonon-induced nematic superconductivity in a topological superconductor candidate Sr $_{0.1}$ Bi $_{2}$ Se $_{3}$

Wang, J.*; Ran, K.*; Li, S.*; Ma, Z.*; Bao, S.*; Cai, Z.*; Zhang, Y.*; 中島健次; 河村聖子; ermk, P.*; et al.

Nature Communications (Internet), 10, p.2802_1 - 2802_6, 2019/06

https://doi.org/10.1038/s41467-019-10942-2

被引用回数：22 パーセンタイル：78.96(Multidisciplinary Sciences)

Superconductivity mediated by phonons is typically conventional, exhibiting a momentum-independent -wave pairing function, due to the isotropic interactions between electrons and phonons along different crystalline directions. Here, by performing inelastic neutron scattering measurements on a superconducting single crystal of Sr $_{0.1}$ Bi $_{2}$ Se $_{3}$ , a prime candidate for realizing topological superconductivity by doping the topo-logical insulator Bi $_{2}$ Se $_{3}$ , we found that there exist singular phonons, with the linewidths of the acoustic phonons increasing substantially at long wavelengths, but only for those along the [001] direction. This observation indicates a large and singular electron-phonon coupling at small momenta, which we propose to give rise to the exotic -wave nematic superconducting pairing in the MxBi $_{2}$ Se $_{3}$ (M = Cu, Sr, Nb) superconductor family. Therefore, we show that these superconductors may be the first examples where electron-phonon interaction can induce more exotic superconducting pairing than the -wave.

論文

Uniaxial pressure effect on the magnetic ordered moment and transition temperatures in BaFe $_{2-x}$ T $_{x}$ As $_{2}$ ( = Co,Ni)

Tam, D. M.*; Song, Y.*; Man, H.*; Cheung, S. C.*; Yin, Z.*; Lu, X.*; Wang, W.*; Frandsen, B. A.*; Liu, L.*; Gong, Z.*; et al.

Physical Review B, 95(6), p.060505_1 - 060505_6, 2017/02

https://doi.org/10.1103/PhysRevB.95.060505

被引用回数：23 パーセンタイル：69.35(Materials Science, Multidisciplinary)

We use neutron diffraction and muon spin relaxation to study the effect of in-plane uniaxial pressure on the antiferromagnetic (AF) orthorhombic phase in BaFe $_{2-x}$ T $_{x}$ As $_{2}$ and its Co- and Ni-substituted members near optimal superconductivity. In the low-temperature AF ordered state, uniaxial pressure necessary to detwin the orthorhombic crystals also increases the magnetic ordered moment, reaching an 11% increase under 40 MPa for BaFe $_{1.9}$ Co $_{0.1}$ As, and a 15% increase for BaFe $_{1.915}$ Ni $_{0.085}$ As. We also observe an increase of the AF ordering temperature () of about 0.25 K/MPa in all compounds, consistent with density functional theory calculations that reveal better Fermi surface nesting for itinerant electrons under uniaxial pressure. The doping dependence of the magnetic ordered moment is captured by combining dynamical mean field theory with density functional theory, suggesting that the pressure-induced moment increase near optimal superconductivity is closely related to quantum fluctuations and the nearby electronic nematic phase.

論文

Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning

Frandsen, B. A.*; Liu, L.*; Cheung, S. C.*; Guguchia, Z.*; Khasanov, R.*; Morenzoni, E.*; Munsie, T. J. S.*; Hallas, A. M.*; Wilson, M. N.*; Cai, Y.*; et al.

Nature Communications (Internet), 7, p.12519_1 - 12519_8, 2016/08

https://doi.org/10.1038/ncomms12519

被引用回数：34 パーセンタイル：76.48(Multidisciplinary Sciences)

RENiO (RE = rare-earth element) and VO are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO) or pressure (VO), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation experiments that the QPT in RENiO and VO is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.

論文

Electronic excitations around the substituted atom in LaCu $_{1-y}$ NO as seen via resonant inelastic X-ray scattering

石井賢司; 筒井健二; 池内和彦*; Jarrige, I.; 水木純一郎; 平賀晴弘*; 山田和芳*; 遠山貴己*; 前川禎通; 遠藤康夫*; et al.

Physical Review B, 85(10), p.104509_1 - 104509_5, 2012/03

https://doi.org/10.1103/PhysRevB.85.104509

被引用回数：3 パーセンタイル：14.19(Materials Science, Multidisciplinary)

We perform a resonant inelastic X-ray scattering (RIXS) study of Ni-substituted LaCuO and Cu-substituted LaNiO.Resonantly enhanced charge-transfer excitations are successfully observed by tuning the incident photon energy to the -edge of the substituted element. These excitations display a very weak momentum dependence, evidencing their local character. We find a shift in the energy of the onset edge of these features compared with the non-substituted compounds LaCuO and LaNiO. This shift is quantitatively reproduced by exact diagonalization calculations of the RIXS spectra. RIXS is shown to be a powerful tool to probe the electronic states of substituted elements and to understand their interaction with surrounding atoms.

論文

Resonant inelastic X-ray scattering of LaCu $_{0.95}$ Ni $_{0.05}$ O

石井賢司; 池内和彦*; Jarrige, I.; 水木純一郎; 平賀晴弘*; 山田和芳*; 筒井健二; 遠山貴己*; 前川禎通*; 遠藤康夫*; et al.

Physica C, 470(Suppl.1), p.S155 - S157, 2010/12

https://doi.org/10.1016/j.physc.2009.11.171

被引用回数：0 パーセンタイル：0.00(Physics, Applied)

Substitution of a specific element for a component is often used to elucidate its role in the superconductors. For a complete understanding of the substitution effect not only on the superconductivity but also on the electronic states, element-selective experiments are required. In this respect, resonant inelastic X-ray scattering (RIXS) has proven to be a powerful experimental technique enabling element-selective diagnosis of charge excitations. By tuning the incident photon energy to a given absorption edge of the element, the excitations involving the element are resonantly enhanced. In addition, RIXS has the advantage that momentum dependence can be measured. Using RIXS, we have measured the electronic excitations at the substituting sites in LaCu $_{0.95}$ Ni $_{0.05}$ O and LaNi $_{0.95}$ Cu $_{0.05}$ O. Near the absorption edge of the substituting element, namely the Ni -edge for LaCu $_{0.95}$ Ni $_{0.05}$ O and the Cu -edge for LaNi $_{0.95}$ Cu $_{0.05}$ O, charge transfer excitations from the 2 level of neighboring oxygen to the upper Hubbard band of the substituted Ni/Cu are observed. Experimental spectra are qualitatively reproduced by a theoretical calculation based on a - model.

論文

Thermally activated charge transfer in a Prussian blue derivative probed by resonant inelastic X-ray scattering

Jarrige, I.; Cai, Y. Q.*; 石井啓文*; 平岡望*; Bleuzen, A.*

Applied Physics Letters, 93(5), p.054101_1 - 054101_3, 2008/08

https://doi.org/10.1063/1.2966355

被引用回数：9 パーセンタイル：36.02(Physics, Applied)

Charge-transfer excitation is at the source of the photoinduced magnetism observed in several Prussian blue molecule-based magnets. Using resonant inelastic X-ray scattering and X-ray absorption spectroscopy, we probe directly the thermally-activated charge transfer in a photomagnetic Fe-Co cyanide, Cs $_{0.7}$ Co $_{4}$ [Fe(CN) $_{6}$ ] $_{2.9}$ [V] $_{1.1}$ . 16H $_{2}$ O, where [V] represents [Fe(CN) $_{6}$ ] vacancies. The temperature dependence of both Co and Fe valence ratios is estimated for the first time in one cooling run, thus yielding a more complete picture of the temperature-induced cooperative electronic modifications. This novel approach, benefiting from relatively short acquisition times, opens the possibility for realtime characterization of the photoinduced magnetism in molecule-based magnets.

口頭

Electronic excitations probed with resonant inelastic X-ray scattering

石井賢司; 筒井健二; 池内和彦*; Jarrige, I.; 水木純一郎; 平賀晴弘*; 山田和芳*; 遠山貴己*; 前川禎通; 石井啓文*; et al.

no journal, ,

It is widely recognized that inelastic scattering of neutron and X-ray is a powerful tool to investigate dynamical properties of electrons in the energy-momentum space. Especially, inelastic X-ray scattering has become available in the last decade by utilizing brilliant synchrotron radiation X-rays. When the incident X-ray energy is tuned to an absorption edge of a constituent element of materials, resonantly enhanced electronic excitations are observed, which is called resonant inelastic X-ray scattering (RIXS). An additional characteristic arises from the resonant process, namely, the specific element selectively get involved in the observed excitations. While neutron scattering is predominantly sensitive to spin excitations, one can complementarily measure various excitations of electronic degrees of freedom, charge, spin, and orbital, with the RIXS technique. In our presentation, we show an explicit application of the element selectivity: resonant inelastic X-ray scattering of Ni-substituted La $_{2}$ CuO $_{4}$ and Cu-substituted La $_{2}$ NiO $_{4}$ . Resonantly enhanced charge-transfer excitations are successfully observed by tuning the incident photon energy to the K-edge of the substituted element. Combined with theoretical calculations, we will discuss the local electronic states around the substituted element which are affected through the interaction with surrounding atoms.

口頭

Competition between multi-channel Kondo effect and f delocalization in TmTe at high pressure

Jarrige, I.; Rueff, J.-P.*; Shieh, S.*; 田口宗孝*; 石井啓文*; Cai, Y. Q.*

no journal, ,

Identifying the mechanism of Kondo phenomena is arguably one of the most exciting and widely studied issues in condensed matter physics. Intermediate-valent Tm compounds stand out as potential candidates for multichannel Kondo (ncK) effect, since both integer valences Tm $^{2+}$ and Tm $^{3+}$ are magnetic. Using resonant inelastic X-ray scattering and the Anderson impurity model, we probed the Tm valence and 4f-5d hybridization in the high-pressure intermediate-valent TmTe compound. Our results reveal that the f delocalization is discontinuous, characterized by a previously unobserved plateau-like behavior over the 4.36.5 GPa range. This is at odds with the usual, continuous Kondo-like f delocalization, and is interpreted as an experimental observation of the effect of culminating ncK scattering of d electrons from local moments on the electronic structure.

口頭

Ni置換LaCuOの共鳴非弾性X線散乱

石井賢司; 池内和彦; Jarrige, I.; 水木純一郎; 平賀晴弘*; 山田和芳*; 筒井健二; 遠山貴己*; 前川禎通*; 石井啓文*; et al.

no journal, ,

これまでに高温超伝導体のCuをNiに置換した系は非常に数多くの研究がなされてきた。その多くはCu $^{2+}$ ()をNi $^{2+}$ ()に置換したと考え、Niを磁性不純物として着目したものであったが、Ni置換は電子状態にも何らかの影響があると予想される。今回、共鳴非弾性X線散乱(RIXS)の元素選択性を利用することによりNi周りの電子状態を抽出することに成功したのでその結果について報告する。本研究で用いた吸収端のRIXSでは、CuまたはNiの-遷移に対応するエネルギーのX線を利用することで、電荷ギャップを越える励起が観測できる。例えば、Niの吸収端でLaCu $_{0.95}$ Ni $_{0.05}$ Oの測定を行うと、中間状態で生成されたNiの正孔を遮蔽するために周りの酸素軌道からNiの軌道へ電子が遷移する。酸素軌道にできたホールはCuとZhang-Rice siglet(ZRS)を形成するので、ZRSとNi()が存在するような励起状態を観測することになる。同様に、LaCuOをCuの吸収端で測定すると、ZRSとCu( $3d^{10}$ )が生じる励起状態が観測される。今回、LaCu $_{1-y}$ NiOのの測定を行い、既に報告されているのスペクトルと比較することで、Ni, Cuそれぞれに特徴的な電子状態の議論を行う。

口頭

Radiation-induced degradation of cellulose in the 1-butyl-3-methylimidazolium chloride ionic liquid

Peng, J.; Cai, D.*; Hao, Y.*; Zhai, M.*; Lin, M.; 勝村庸介

no journal, ,

イオン液体である1-ブチル-3-メチルイミダゾリウムクロライド([Bmim]Cl)はセルロースを特別な誘導体にせずとも溶かすほど、溶解性に優れている。ここでは、[Bmim]Cl中に溶解した微結晶セルロースの線照射後の分子量測定を行った。微結晶セルロースの線照射分解を検討し、分解のG値,Gdを算出した。