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論文

Impact of the Ce$$4f$$ states in the electronic structure of the intermediate-valence superconductor CeIr$$_3$$

藤森 伸一; 川崎 郁斗; 竹田 幸治; 山上 浩志; 雀部 矩正*; 佐藤 芳樹*; 清水 悠晴*; 仲村 愛*; Maruya, A.*; 本間 佳哉*; et al.

Electronic Structure (Internet), 5(4), p.045009_1 - 045009_7, 2023/11

The electronic structure of the $$f$$-based superconductor $$mathrm{CeIr_3}$$ was studied by photoelectron spectroscopy. The energy distribution of the $$mathrm{Ce}~4f$$ state was revealed by the $$mathrm{Ce}~3d-4f$$ resonant photoelectron spectroscopy. The $$mathrm{Ce}~4f$$ state was mostly distributed in the vicinity of the Fermi energy, suggesting the itinerant character of the $$mathrm{Ce}~4f$$ state. The contribution of the $$mathrm{Ce}~4f$$ state to the density of states (DOS) at the Fermi energy was estimated to be nearly half of that of the$$mathrm{Ir}~5d$$ states, implying that the $$mathrm{Ce}~4f$$ state has aconsiderable contribution to the DOS at the Fermi energy. The $$mathrm{Ce}~3d$$ core-level and $$mathrm{Ce}~3d$$ X-ray absorption spectra were analyzed based on a single-impurity Anderson model. The number of the $$mathrm{Ce}~4f$$ state in the ground state was estimated to be 0.8-0.9, which is much larger than the values obtained in the previous studies (i.e., 0-0.4).

論文

Magnetic and fermi surface properties of semimetals EuAs$$_3$$ and Eu(As$$_{1-x}$$P$$_x$$)$$_3$$

大貫 惇睦*; 軽部 皓介*; 青木 大*; 仲村 愛*; 本間 佳哉*; 松田 達磨*; 芳賀 芳範; 竹内 徹也*

Journal of the Physical Society of Japan, 92(11), p.114703_1 - 114703_12, 2023/11

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

Single crystal samples of a series of semimetallic magnet Eu(As$$_{1-x}$$P$$_x$$)$$_3$$ have successfully grown. By measuring magnetization, Hall resistivity and de Haas-van Alphen oscillations, large anomalous Hall resistivity arising from peculiar magnetic phase diagram was identified.

論文

Superconducting spin reorientation in spin-triplet multiple superconducting phases of UTe$$_2$$

金城 克樹*; 藤林 裕己*; 松村 拓輝*; 堀 文哉*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; et al.

Science Advances (Internet), 9(30), p.2736_1 - 2736_6, 2023/07

 被引用回数:7 パーセンタイル:84.75(Multidisciplinary Sciences)

Superconducting (SC) state has spin and orbital degrees of freedom, and spin-triplet superconductivity shows multiple SC phases because of the presence of these degrees of freedom. However, the observation of spin-direction rotation occurring inside the SC state (SC spin rotation) has hardly been reported. Uranium ditelluride, a recently found topological superconductor, exhibits various SC phases under pressure: SC state at ambient pressure (SC1), high-temperature SC state above 0.5 gigapascal (SC2), and low-temperature SC state above 0.5 gigapascal (SC3). We performed nuclear magnetic resonance (NMR) and ac susceptibility measurements on a single-crystal uranium ditelluride. The b axis spin susceptibility remains unchanged in SC2, unlike in SC1, and decreases below the SC2-SC3 transition with spin modulation. These unique properties in SC3 arise from the coexistence of two SC order parameters. Our NMR results confirm spin-triplet superconductivity with SC spin parallel to b axis in SC2 and unveil the remaining of spin degrees of freedom in SC uranium ditelluride.

報告書

HTTR広領域中性子検出器の開発; 熱サイクル負荷に対する耐熱性能の向上

小澤 太教; 菅沼 拓朗; 本間 史隆; 東村 圭祐*; 鵜飼 隆由*; 齋藤 賢司

JAEA-Technology 2023-007, 24 Pages, 2023/06

JAEA-Technology-2023-007.pdf:2.24MB

HTTR広領域中性子検出器の高温環境下における信頼性向上を目的として、広領域中性子検出器の構造変更を検討した結果、リード線によってMIケーブル芯線と金属管を接合する構造を廃止し、MIケーブル芯線と金属管を直接接合する構造が短時間で対応できる最も信頼性が高い方法であることが明らかとなった。この方法で接続部分のモックアップを製作して熱サイクル試験及び高温耐久試験を実施した結果、HTTRの使用条件においても接続部分の健全性が保たれることが明らかとなった。

論文

Low-temperature magnetic fluctuations investigated by $$^{125}$$Te-NMR on the uranium-based superconductor UTe$$_2$$

藤林 裕己*; 金城 克樹*; 仲嶺 元輝*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; 清水 悠晴*; et al.

Journal of the Physical Society of Japan, 92(5), p.053702_1 - 053702_5, 2023/05

 被引用回数:5 パーセンタイル:77.22(Physics, Multidisciplinary)

To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe$$_2$$, we measured the NMR Knight shift $$K$$ and the nuclear spin lattice relaxation rate 1/$$T_1$$ in $$H//a$$ by $$^{125}$$Te-NMR on a $$^{125}$$Te-enriched single-crystal sample. 1/$$T_1$$$$T$$ in $$H//a$$ is much smaller than 1/$$T_1$$$$T$$ in $$H //b$$ and c, and magnetic fluctuations along each axis are derived from the 1/$$T_1$$$$T$$ measured in $$H$$ parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed.

論文

Large reduction in the $$a$$-axis knight shift on UTe$$_2$$ with $$T_c$$ = 2.1 K

松村 拓輝*; 藤林 裕己*; 金城 克樹*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; 清水 悠晴*; et al.

Journal of the Physical Society of Japan, 92(6), p.063701_1 - 063701_5, 2023/05

 被引用回数:27 パーセンタイル:97.99(Physics, Multidisciplinary)

Spin susceptibility in the superconducting (SC) state was measured in the higher-quality sample of uranium-based superconductor UTe$$_2$$ by using Knight-shift measurements for a magnetic field $$H$$ along all three crystalline axes. In the higher-quality sample, the SC transition temperature $$T_c$$ is about 2.1 K, and the residual electronic term in the specific heat is almost zero. The NMR linewidth becomes narrower and is almost half of that in the previous sample with $$T_csim$$1.6 K when $$H//a$$ and $$c$$. Although the Knight-shift behavior was not so different from the previous results for $$H//b$$, and $$c$$, a large reduction in Knight shift along the $$a$$ axis was observed, in contrast with the previous $$a$$-axis Knight shift result. We discuss the origin of the difference between the previous and present results, and the possible SC state derived from the present results.

論文

Change of superconducting character in UTe$$_{2}$$ induced by magnetic field

金城 克樹*; 藤林 裕己*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; 清水 悠晴*; 本間 佳哉*; et al.

Physical Review B, 107(6), p.L060502_1 - L060502_5, 2023/02

 被引用回数:18 パーセンタイル:94.24(Materials Science, Multidisciplinary)

UTe$$_2$$ is a recently discovered spin-triplet superconductor. One of the characteristic features of UTe$$_2$$ is a magnetic field ($$H$$)-boosted superconductivity above 16 T when H is applied exactly parallel to the $$b$$ axis. To date, this superconducting (SC) state has not been thoroughly investigated, and the SC properties as well as the spin state of this high-$$H$$ SC (HHSC) phase are not well understood. In this letter, we performed AC magnetic susceptibility and nuclear magnetic resonance measurements and found that, up to 24.8 T, the HHSC state has bulk nature and is quite sensitive to the $$H$$ angle and that its SC character is different from that in the low-$$H$$ SC (LHSC) state. The dominant spin component of the spin-triplet pair is along the $$a$$ axis in the LHSC state but is changed in the HHSC state along the $$b$$ axis. Our results indicate that $$H$$-induced multiple SC states originate from the remaining spin degrees of freedom.

論文

First observation of the de Haas-van Alphen effect and Fermi surfaces in the unconventional superconductor UTe$$_2$$

青木 大*; 酒井 宏典; Opletal, P.; 常盤 欣文; 石塚 淳*; 柳瀬 陽一*; 播磨 尚朝*; 仲村 愛*; Li, D.*; 本間 佳哉*; et al.

Journal of the Physical Society of Japan, 91(8), p.083704_1 - 083704_5, 2022/08

 被引用回数:47 パーセンタイル:98.21(Physics, Multidisciplinary)

de Haas-van Alphen oscillation was successfully observed in an unconventional superconductor UTe$$_2$$ using high-quality single crystals. From this observation, Fermi surfaces of this compound were determined to be cylinders elongated along the c-direction, in consistent with theoretical expectation. However, the extremely large cyclotron effective masses ranging 32 to 57 m$$_0$$, in consistent with the electronic specific heat, far exceed calculated values.

論文

Drastic change in magnetic anisotropy of UTe$$_2$$ under pressure revealed by $$^{125}$$Te-NMR

金城 克樹*; 藤林 裕己*; 仲嶺 元輝*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; 清水 悠晴*; et al.

Physical Review B, 105(14), p.L140502_1 - L140502_5, 2022/04

 被引用回数:7 パーセンタイル:61.70(Materials Science, Multidisciplinary)

To investigate the normal-state magnetic properties of UTe$$_2$$ under pressure, we perform $$^{125}$$Te nuclear magnetic resonance (NMR) measurements up to 2 GPa. Below 1.2 GPa, the b-axis NMR Knight shift shows a broad maximum at the so-called $$T_{chi, max}$$ on cooling, which is consistent with the magnetization measurement under pressure. $$T_{chi, max}$$ decreases with increasing pressure and disappears at the critical pressure $$P_c$$= 1.7 GPa, above which superconductivity is destroyed.

論文

Improving the safety of the high temperature gas-cooled reactor "HTTR" based on Japan's new regulatory requirements

濱本 真平; 清水 厚志; 猪井 宏幸; 栃尾 大輔; 本間 史隆; 澤畑 洋明; 関田 健司; 渡辺 周二; 古澤 孝之; 飯垣 和彦; et al.

Nuclear Engineering and Design, 388, p.111642_1 - 111642_11, 2022/03

 被引用回数:3 パーセンタイル:50.01(Nuclear Science & Technology)

日本原子力研究開発機構は、2011年の福島第一原子力発電所事故を契機に作られ2013年12月に施行された新しい規制要件に、高温工学試験研究炉(HTTR)を適合させた。様々な高温ガス炉(HTTR)安全試験を通じて得られたHTGRに関する知見を基に、既存の構造物,系統及び機器の安全性及び耐震分類が議論された。防護の対象となる構築物,系統及び機器が再検討し、安全機能に影響を及ぼす内的・外的脅威への対策が強化された。さらに、設計基準を超える事故として、多量の放射性物質が放出されるおそれのある事故に対する措置を講じた。我々のこの対応が、新しい規制要求に適合していることを、原子力規制委員会は厳格かつ適切に審査した。2014年11月に提出したHTTRの設置許可変更申請書は、9回の修正を経て2020年6月に承認された。この対応は、高温ガス炉の特性を反映すれば、強化された規制要件を満たすためでも合理的に設計できることを示しており、今後の高温ガス炉の開発の参考になると考える。

論文

Ten years since the Fukushima Daiichi NPP disaster; What's important when protecting the population from a multifaceted technological disaster

Callen-Kovtunova, J.*; 本間 俊充

International Journal of Disaster Risk Reduction (Internet), 70, p.102746_1 - 102746_10, 2022/02

 被引用回数:3 パーセンタイル:29.57(Geosciences, Multidisciplinary)

本論文は、福島第一原子力発電所事故で確認された原子力発電所事故による緊急事態の公衆防護に関する主要な教訓を提示している。事故前の緊急事態の取り決め、緊急事態時に何が起こったか、そして得られた教訓を記述している。論文では、線量予測モデルの失敗、防護措置を考慮すべき範囲など予め準備すべき重要な課題について強調している。また、特に病院や高齢者施設からの弱者の安全な避難の取り決めの必要性など過去に見過ごされたてきた教訓も提示した。

論文

Speciation on the reaction of uranium and zirconium oxides treated under oxidizing and reducing atmospheres

上原 章寛*; 秋山 大輔*; 池田 篤史; 沼子 千弥*; 寺田 靖子*; 新田 清文*; 伊奈 稔哲*; 武田 志乃*; 桐島 陽*; 佐藤 修彰*

Journal of Nuclear Materials, 559, p.153422_1 - 153422_11, 2022/02

 被引用回数:4 パーセンタイル:50.01(Materials Science, Multidisciplinary)

The reaction products were analysed by a combination of powder X-ray diffraction (PXRD) and X-ray absorption spectroscopic measurements of the U L$$_{rm III}$$- and Zr K-edges. Under an oxidizing atmosphere, the formation of U$$_{3}$$O$$_{8}$$ and U$$_{2}$$Zr$$_{5}$$O$$_{15}$$ was observed in equilibrium with UO$$_{2}$$, monoclinic-ZrO$$_{2}$$, and tetragonal-ZrO$$_{2}$$. However, when O$$_{2}$$ gas was purged through the reaction tube during the cooling process to room temperature, pentavalent U in ZrU$$_{2}$$O$$_{7}$$ was produced by the oxidation of solid solution UO$$_{2}$$ formed at $$>$$ 1774 K during the temperature dropped at $$<$$ 1473 K. Under the inert atmosphere, mixed oxides of uranium were found to form at $$>$$ 1673 K due to a low concentration of O$$_{2}$$ impurity with the Ar gas. This study can pave the way for understanding the interaction between the nuclear fuels and the cladding materials in damaged reactors enabling further simulation of possible decontamination procedures.

論文

Slow electronic dynamics in the paramagnetic state of UTe$$_2$$

徳永 陽; 酒井 宏典; 神戸 振作; 芳賀 芳範; 常盤 欣文; Opletal, P.; 藤林 裕己*; 金城 克樹*; 北川 俊作*; 石田 憲二*; et al.

Journal of the Physical Society of Japan, 91(2), p.023707_1 - 023707_5, 2022/02

 被引用回数:22 パーセンタイル:92.14(Physics, Multidisciplinary)

ウラン系の強磁性超伝導体で議論されてきた、「強磁性ゆらぎによるスピン三重項超伝導対の形成」および「強磁性ゆらぎを介した磁場による対形成引力の制御」というコンセプトがUTe$$_2$$においても成り立つことを期待させる。しかしその一方、$$_2$$では静的な強磁性秩序は存在せず、低温の磁気状態がこれまでのウラン系強磁性超伝導体にどこまで近いのかという点については疑問を持たれていた。実際、最近の中性子散乱実験では、比較的高温側から反強磁性に近いq=0.57という波数を持った磁気ゆらぎの発達が示されている。本研究では$$^{125}$$Te-NMR実験により低温で非常に遅いゆっくりとした揺らぎが発達する様子を捉えることに成功した。このことはこの系の低温における強い相関の発達を示唆している。

論文

Observation of longitudinal magnetic fluctuations at a first-order ferromagnetic quantum phase transition in UGe$$_2$$

野間 雄一郎*; 小手川 恒*; 久保 徹郎*; 藤 秀樹*; 播磨 尚朝*; 芳賀 芳範; 山本 悦嗣; 大貫 惇睦*; 伊藤 公平*; 仲村 愛*; et al.

Journal of the Physical Society of Japan, 90(7), p.073707_1 - 073707_5, 2021/07

 被引用回数:1 パーセンタイル:13.00(Physics, Multidisciplinary)

Ferromagnetic fluctuation relevant to the pressure-induced superconductivity in UGe$$_2$$ is investigated by means of NMR spectroscopy. Longitudinal magnetic fluctuations were observed in the spin-echo decay rate near the ferromagnetic critical point where superconductivity takes place. This result strongly suggests that superconductivity in ferromagnets is universally mediated by anisotropic magnetic fluctuations.

論文

Critical slowing-down and field-dependent paramagnetic fluctuations in the skyrmion host EuPtSi; $$mu$$SR and NMR studies

比嘉 野乃花*; 伊藤 孝; 與儀 護*; 服部 泰佑; 酒井 宏典; 神戸 振作; Guguchia, Z.*; 髭本 亘; 中島 美帆*; 本間 佳哉*; et al.

Physical Review B, 104(4), p.045145_1 - 045145_7, 2021/07

 被引用回数:2 パーセンタイル:12.59(Materials Science, Multidisciplinary)

We report the results of $$mu$$SR and $$^{29}$$Si NMR measurements carried out on the cubic chiral magnet EuPtSi. Our zero-field $$mu$$SR experiments revealed the development of critical slowing down of Eu spin fluctuations over a relatively wide critical region above $$T_N$$. We also found from $$^{29}$$Si NMR that the spin fluctuations are strongly suppressed by magnetic field in the paramagnetic state above 20K. These characteristic spin dynamics observed over a wide region of temperature and magnetic field suggest the presence of magnetic frustration in the spin system. Such frustration would underlie the mechanism stabilizing the short-period skyrmion lattice observed in this compound.

論文

Inhomogeneous superconducting state probed by $$^{125}$$Te NMR on UTe$$_2$$

仲嶺 元輝*; 金城 克樹*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; 清水 悠晴*; 本間 佳哉*; et al.

Journal of the Physical Society of Japan, 90(6), p.064709_1 - 064709_7, 2021/06

 被引用回数:23 パーセンタイル:85.83(Physics, Multidisciplinary)

UTe$$_2$$ is a recently discovered promising candidate for a spin-triplet superconductor. In contrast to conventional spin-singlet superconductivity, spin-triplet superconductivity possesses spin and angular momentum degrees of freedom. We previously reported that the shoulder signal appears in NMR spectra below the superconducting (SC) transition temperature $$T_c$$ in $$H//b$$, and a slight decrease in the Knight shift along the $$b$$ and $$c$$ axes ($$K_{rm b}$$ and $$K_{rm c}$$, respectively) below $$T_c$$ at a low magnetic field $$H$$. Although the decrease in $$K_{rm c}$$ vanished above 5.5 T, the decrease in $$K_{rm b}$$ was independent of $$H$$ up to 6.5 T. To clarify the origin of the shoulder signal and the trace of the decrease in $$K_{rm b}$$, we compared the $$^{125}$$Te-NMR spectra obtained when $$H//b$$ and $$H//c$$ and measured the $$^{125}$$Te-NMR spectra for $$H//b$$ up to 14.5 T.

論文

原子力災害の防護方策の意思決定; リスクトレードオフとステークホルダー関与

神田 玲子*; 本間 俊充*; 高原 省五; 坪倉 正治*; 大迫 政浩*; 川口 勇生*; 加藤 尊秋*

リスク学研究, 30(3), p.133 - 139, 2021/04

東京電力福島第一原子力発電所(1F)事故から約10年が経過し、原子力災害時における防護措置について多くの経験が蓄積されてきた。1F事故後の防護措置では、住民へのパターナリスティックな介入や脆弱な集団の避難による健康リスクの増加などの問題が明らかになった。また、除染等の長期的な管理においても、次世代や県外の住民等のステークホルダー間において、リスク・トレードオフが発生しており複雑で継続的な課題と向き合うことになる。これらの事例は、原子力災害の特徴としてリスクが地理的にも時間的にも広範にわたるため、現実の対応では個々の事例に則した対応が不可欠であることを示している。今後、原子力防災の改善にあたっては、国等による合理的な防災計画に加えて住民等の理解や考え方を防災計画に反映することで、トップダウン的アプローチとボトムアップ的アプローチをバランスよく取り入れていく必要がある。

論文

Anisotropic response of spin susceptibility in the superconducting state of UTe$$_2$$ probed with $$^{125}$$Te-NMR measurement

仲嶺 元輝*; 金城 克樹*; 北川 俊作*; 石田 憲二*; 徳永 陽; 酒井 宏典; 神戸 振作; 仲村 愛*; 清水 悠晴*; 本間 佳哉*; et al.

Physical Review B, 103(10), p.L100503_1 - L100503_5, 2021/03

 被引用回数:43 パーセンタイル:93.08(Materials Science, Multidisciplinary)

To investigate spin susceptibility in a superconducting (SC) state, we measured the $$^{125}$$Te-NMR Knight shifts at magnetic fields ($$H$$) up to 6.5 T along the $$b$$ and $$c$$ axes of single-crystal UTe$$_2$$, a promising candidate for a spin-triplet superconductor. In the SC state, the Knight shifts along the $$b$$ and $$c$$ axes ($$K_{rm b}$$ and $$K_{rm c}$$, respectively) decreased slightly, and the decrease in $$K_{rm b}$$ was almost constant up to 6.5 T. The reduction in $$K_{rm c}$$ decreased with increasing $$H$$, and $$K_{rm c}$$ was unchanged through the SC transition temperature at 5.5 T, excluding the possibility of spin-singlet pairing. Our results indicate that spin susceptibilities along the $$b$$ and $$c$$ axes slightly decrease in the SC state in low $$H$$, and the $$H$$ response of SC spin susceptibility is anisotropic on the $$bc$$ plane.

論文

Single-crystal growth and magnetic phase diagram of the enantiopure crystal of NdPt$$_2$$B

佐藤 芳樹*; 本多 史憲*; Maurya, A.*; 清水 悠晴*; 仲村 愛*; 本間 佳哉*; Li, D.*; 芳賀 芳範; 青木 大*

Physical Review Materials (Internet), 5(3), p.034411_1 - 034411_9, 2021/03

 被引用回数:2 パーセンタイル:9.72(Materials Science, Multidisciplinary)

Single-crystal growth and magnetic properties of NdPt$$_2$$B are reported on a enantiopure crystal. We observed multiple phase transitions at 9.5 and 11 K under zero magnetic field. Nontrivial magnetic phase diagram demonstrates the competitive interactions in this system.

論文

Core-level photoelectron spectroscopy study of UTe$$_{2}$$

藤森 伸一; 川崎 郁斗; 竹田 幸治; 山上 浩志; 仲村 愛*; 本間 佳哉*; 青木 大*

Journal of the Physical Society of Japan, 90(1), p.015002_1 - 015002_2, 2021/01

 被引用回数:20 パーセンタイル:83.99(Physics, Multidisciplinary)

The valence state of $$mathrm{UTe}_2$$ was studied by core-level photoelectron spectroscopy. The main peak position of the $$mathrm{U}~4f$$ core-level spectrum of $$mathrm{UTe}_2$$ coincides with that of $$mathrm{UB}_2$$, which is anitinerant compound with a nearly $$5f^3$$ configuration. However, the main peak of $$mathrm{UTe}_2$$ is broader than that of$$mathrm{UB}_2$$, and satellite structures are observed in the higher binding energy side of the main peak, which are characteristics of mixed-valence uranium compounds. These results suggest that the $$mathrm{U}~5f$$ state in $$mathrm{UTe}_2$$ isin a mixed valence state with a dominant contribution from the itinerant$$5f^3$$ configuration.

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