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論文

Application of energy-resolving neutron imaging to major-component analyses of materials using four-channel superconducting detector

Vu, TheDang*; 宍戸 寛明*; 相澤 一也; 奥 隆之; 及川 健一; 原田 正英; 小嶋 健児*; 宮嶋 茂之*; 曽山 和彦; 小山 富男*; et al.

IEEJ Transactions on Electrical and Electronic Engineering, 19(11), p.1888 - 1894, 2024/11

 被引用回数:0 パーセンタイル:0.00(Engineering, Electrical & Electronic)

We proposed a novel superconducting detector called the current-biased kinetic inductance detector (CB-KID) for constructing a neutron transmission imager. We systematically studied the characteristics of the CB-KID to improve spatial resolution down to 10 $$mu$$m in transmission imaging. By analyzing neutron transmission spectra from 1 meV to 500 keV, we identified copper (Cu) and iron (Fe) as major components in commercial nuts and screws. Additionally, we successfully mapped the distribution of the SmSn$$_{3}$$ compound using selective energy regions of pulsed neutrons and the CB-KID detector. It can reveal transmission spectra across a wide range of energies, from cold-neutron energies (meV) to higher neutron energies (up to 500 keV).

報告書

SIMMER-III and SIMMER-IV; Computer codes for LMFR core disruptive accident analysis

近藤 悟; 飛田 吉春*; 守田 幸路*; 神山 健司; 山野 秀将; 鈴木 徹*; 田上 浩孝; 曽我部 丞司; 石田 真也

JAEA-Research 2024-008, 235 Pages, 2024/10

JAEA-Research-2024-008.pdf:4.77MB

日本原子力研究開発機構が開発したSIMMER-III及びSIMMER-IVは、2次元/3次元、多速度場、多成分流体力学モデルを空間・時間依存の核動特性モデルと結合した計算コードであり、液体金属高速炉の炉心崩壊事故の解析に広く利用されている。従来コードに対して次のような高度化したモデルが採用されている。すなわち、安定かつ頑健な流体力学アルゴリズム、最大8までの多速度場モデル、構造材及び多相流幾何形状の取扱いの改善、熱及び質量移行過程の包括的取扱い、高精度の状態方程式、高精度かつ高効率の中性子束計算モデル、崩壊熱モデルなどである。本報告書ではSIMMER-III及びSIMMER-IVのモデル及び解法の詳細を記述する。別途詳細が報告されている個別モデルについてはその概要をまとめる。なお、コードの検証及び妥当性確認についてはすでに報告済みである。

論文

France-Japan collaboration on severe accident studies in sodium-cooled fast reactors, 1; Severe accident scenarios assessment

小野田 雄一; 石田 真也; 深野 義隆; 神山 健司; 山野 秀将; 久保 重信; 柴田 明裕*; Bertrand, F.*; Seiler, N.*

Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10

PIRTs have been developed and are reported for the 3 sequence event families of SFR severe accidents. For ULOF, there are 13 phenomena ranked with high importance and large uncertainty. Two PIRTs for primary phase of UTOP have been developed based on those of ULOF. Two phenomena with high importance and large uncertainty both in FRN and JPN ranking are highlighted. For USAF PIRT, they are eight phenomena ranked important and uncertain by both sides related to heat transfer coefficient, chunk relocation in the molten pool of the initiating SA and to thermomechanical loading on the hexcan of the initiating SA. These phenomena are recognized to deserve priority study. The event progression regarding FP transport focusing on phenomena of ULOF is investigated. Seven phenomenological phases were identified along with the accident sequences and of their events progression. The summary of the elementary phenomena on this PIRT, and the vote for the table are foreseen in the future study.

論文

Neutron transmission imaging system with a superconducting kinetic inductance detector

Vu, TheDang*; 宍戸 寛明*; 相澤 一也; 奥 隆之; 及川 健一; 原田 正英; 小嶋 健児*; 宮嶋 茂之*; 曽山 和彦; 小山 富男*; et al.

Journal of Physics; Conference Series, 2776, p.012009_1 - 012009_9, 2024/06

We optimized the design and operating conditions of our superconducting neutron detector to improve spatial resolution. We obtained the best spatial resolution of 10 $$mu$$m when a Gd Siemens star pattern was mounted at close contact with the detector in the cryostat. We compared the effect of a different sample-detector distance on a spatial resolution when the samples were placed either at cryogenic temperature or at room temperature. We found the appearance of clear Bragg dips by the measurements of natural FeS$$_{2}$$ single crystals and succeeded in mapping the distribution of differently-oriented crystals by choosing several Bragg dips of the FeS$$_{2}$$ crystals to compose the transmission images.

論文

Neutron transmission CB-KID imager using samples placed at room temperature

石田 武和*; Vu, TheDang*; 宍戸 寛明*; 相澤 一也; 奥 隆之; 及川 健一; 原田 正英; 小嶋 健児*; 宮嶋 茂之*; 小山 富男*; et al.

Journal of Low Temperature Physics, 214(3-4), p.152 - 157, 2024/02

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

We built a new cryostat to apply a current-biased kinetic inductance detector (CB-KID) for conducting neutron transmission imaging of room temperature samples under pulsed neutrons. A Wood's metal alloy of melting temperature 75.2$$^{circ}$$C was placed at room temperature to inspect the measurement system at J-PARC. Since one of the four phases of Wood's metal is a fine Cd-rich needle phase (width $$sim$$ 25 $$mu$$m and length $$sim$$ 5 mm), it is suitable for observing fine mosaic structure selectively by neutron imaging. The spatial resolution of the CB-KID imager was estimated as $$sim$$ 10 $$mu$$m by using a Gd Siemens-star pattern. The CB-KID system is useful to conduct transmission imaging for various materials rather easily at room temperature.

論文

Longitudinal spin fluctuations driving field-reinforced superconductivity in UTe$$_2$$

徳永 陽; 酒井 宏典; 神戸 振作; Opletal, P.; 常盤 欣文; 芳賀 芳範; 北川 俊作*; 石田 憲二*; 青木 大*; Knebel, G.*; et al.

Physical Review Letters, 131(22), p.226503_1 - 226503_7, 2023/12

 被引用回数:6 パーセンタイル:80.90(Physics, Multidisciplinary)

Our measurements of $$^{125}$$Te NMR relaxations reveal an enhancement of electronic spin fluctuations above $$mu_0H^*sim15$$~T, leading to their divergence in the vicinity of the metamagnetic transition at $$mu_0H_mapprox35$$~T, below which field-reinforced superconductivity appears when a magnetic field ($$H$$) is applied along the crystallographic $$b$$ axis. The NMR data evidence that these fluctuations are dominantly longitudinal, providing a key to understanding the peculiar superconducting phase diagram in $$H|b$$, where such fluctuations enhance the pairing interactions.

論文

Orientation mapping of YbSn$$_{3}$$ single crystals based on Bragg-dip analysis using a delay-line superconducting sensor

宍戸 寛明*; Vu, TheDang*; 相澤 一也; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 奥 隆之; 曽山 和彦; 宮嶋 茂之*; et al.

Journal of Applied Crystallography, 56(4), p.1108 - 1113, 2023/08

 被引用回数:1 パーセンタイル:37.25(Chemistry, Multidisciplinary)

Recent progress in high-power pulsed neutron sources has stimulated the development of the Bragg dip and Bragg edge analysis methods using a two-dimensional neutron detector with high temporal resolution to resolve the neutron energy by the time-of-flight method. A delay-line current-biased kinetic inductance detector (CB-KID) is a two-dimensional superconducting sensor with a high temporal resolution and multi-hit capability. Here, it is demonstrated that a delay-line CB-KID with a $$^{10}$$B neutron conversion layer can be applied to high-spatial-resolution neutron transmission imaging and spectroscopy up to 100 eV. Dip structures are observed in the transmission spectra of YbSn$$_{3}$$ single crystals, induced by Bragg diffraction and nuclear resonance absorption. The orientation mapping of YbSn$$_{3}$$ crystals is successfully drawn based on the analysis of observed Bragg dip positions in the transmission spectra.

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:6 パーセンタイル:80.90(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.

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:75.19(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:21 パーセンタイル:97.82(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

NMRで探るウラン系スピン三重項超伝導の物理

徳永 陽; 酒井 宏典; 北川 俊作*; 石田 憲二*

日本物理学会誌, 78(5), p.267 - 272, 2023/04

UTe$$_2$$は2018年末に超伝導になることが初めて報告されたウラン系超伝導体である。その発見の直後から実験と理論の両面での集中的な研究が開始され、40T以上の強磁場領域における磁場誘起超伝導や圧力下での多重超伝導相など、スピン三重項超伝導状態を起源とする新奇な超伝導現象が相次いで見つかっている。さらにその超伝導状態は、バルクとしてトポロジカル超伝導を実現する可能性があることが指摘され注目を集めている。本稿ではこのUTe$$_2$$において、我々が行ってきた核磁気共鳴(NMR)法による研究について紹介する。

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:16 パーセンタイル:95.14(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

The Damage analysis for irradiation tolerant spin-driven thermoelectric device based on single-crystalline Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt heterostructures

家田 淳一; 岡安 悟; 針井 一哉*; 小畠 雅明; 吉井 賢資; 福田 竜生; 石田 真彦*; 齊藤 英治

IEEE Transactions on Magnetics, 58(8), p.1301106_1 - 1301106_6, 2022/08

 被引用回数:1 パーセンタイル:13.68(Engineering, Electrical & Electronic)

スピンゼーベック効果(SSE)に基づくスピン駆動熱電(STE)デバイスと、熱源としての放射性同位元素の組み合わせは、宇宙探査機の電源などの応用における次世代の発電方法としての可能性を秘めている。しかし、スピン熱電デバイスの照射耐性を示す利用可能な知識は非常に限られている。重イオンビーム加速器と硬X線光電子分光法(HAXPES)測定を使用した分析を通じて、Y$$_3$$Fe$$_5$$O$$_{12}$$/Ptヘテロ構造に基づく典型的なSTEデバイスが高エネルギー重イオンビームの照射に対する耐性を持つことを検証する。使用済み核燃料の表面から放出される核分裂生成物による累積損傷をモデル化した320MeVの金イオンビームを使用し、線量レベルを変えることにより、SSE要素の熱電および磁気特性が$$10^{10}$$イオン/cm$$^2$$フルエンスまでのイオン照射線量の影響を受けず、イオントラックがサンプル表面をほぼ完全に覆う約$$10^{12}$$イオン/cm$$^2$$でSSE信号が消滅することを確認した。さらに、HAXPES測定は、Y$$_3$$Fe$$_5$$O$$_{12}$$/Pt界面への影響を理解するために実行した。HAXPES測定は、SSE信号を減少させる化学反応が照射線量の増加とともに強化されることを示唆している。過酷な環境使用に適用できるより優れたSTEデバイスを開発するために、Y$$_3$$Fe$$_5$$O$$_{12}$$/Ptで損傷分析の現在の理解を共有したい。

論文

Unconventional superconductivity in UTe$$_2$$

青木 大*; Brison, J.-P.*; Flouquet, J.*; 石田 憲二*; Knebel, G.*; 徳永 陽; 柳瀬 陽一*

Journal of Physics; Condensed Matter, 34(24), p.243002_1 - 243002_41, 2022/06

 被引用回数:95 パーセンタイル:91.08(Physics, Condensed Matter)

The novel spin-triplet superconductor candidate UTe$$_2$$ attracted enormous attention. We review key experimental and theoretical progress which has been achieved in different laboratories. UTe$$_2$$ has been expected to be close to a ferromagnetic instability, showing many similarities to the U-based ferromagnetic superconductors, URhGe and UCoGe. The competition between different types of magnetic interactions and the duality between the local and itinerant character of the 5 f Uranium electrons, as well as the shift of the U valence appear as key parameters in the rich phase diagrams discovered recently under extreme conditions like low temperature, high magnetic field, and pressure. We discuss macroscopic and microscopic experiments at low temperature to clarify the normal phase properties at ambient pressure for field applied along the three axis of this orthorhombic structure.

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:64.62(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

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:21 パーセンタイル:92.47(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

High spatial resolution neutron transmission imaging using a superconducting two-dimensional detector

宍戸 寛明*; 西村 和真*; Vu, TheDang*; 相澤 一也; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 奥 隆之; 曽山 和彦; et al.

IEEE Transactions on Applied Superconductivity, 31(9), p.2400505_1 - 2400505_5, 2021/12

 被引用回数:0 パーセンタイル:0.00(Engineering, Electrical & Electronic)

中性子イメージングは、重金属に対する高透過性、軽元素に対する高感度、同位体と中性子との特異な核反応による同位体選択性などの中性子ビームの特徴を活かした非破壊検査の有力な手段の一つである。本研究では、超伝導検出器である電流バイアス運動インダクタンス検出器(CB-KID)を用いて、パルス中性子源を用いた飛行時間法による波長分解中性子イメージングを行った。遅延時間型CB-KIDを用いて、GdAl$$_{3}$$単結晶を成長させたGd-Al合金試料の中性子透過像を取得した。その結果、単結晶はAl-Gd合金全体に渡って、形状,分布ともに良好に観察することができた。また、中性子の波長0.03nm以上でGdによる特徴的な中性子の吸収を確認した。さらに、15$$mu$$m$$ times$$ 12$$mu$$mという限られた検出面で、同位体と中性子の核反応によって生じる$$^{155}$$Gd共鳴ディップを観測することができた。また、$$^{155}$$Gdの共鳴ディップを用いてGd選択的イメージングを行ったところ、中性子の波長幅が1pmという限られた範囲で、明確なGd核の元素選択イメージング像を取得することに成功した。

論文

Hybridization of Bogoliubov quasiparticles between adjacent CuO$$_2$$ layers in the triple-layer cuprate Bi$$_2$$Sr$$_2$$Ca$$_2$$Cu$$_3$$O$$_{10+delta}$$ studied by angle-resolved photoemission spectroscopy

出田 真一郎*; Johnston, S.*; 吉田 鉄平*; 田中 清尚*; 森 道康; 安齋 太陽*; 井野 明洋*; 有田 将司*; 生天目 博文*; 谷口 雅樹*; et al.

Physical Review Letters, 127(21), p.217004_1 - 217004_6, 2021/11

 被引用回数:8 パーセンタイル:59.15(Physics, Multidisciplinary)

Hybridization of Bogoliubov quasiparticles (BQPs) between the CuO$$_2$$ layers in the triple-layer cuprate high-temperature superconductor Bi$$_2$$Sr$$_2$$Ca$$_2$$Cu$$_3$$O$$_{10+delta}$$ is studied by angle-resolved photoemission spectroscopy (ARPES). In the superconducting state, an anti-crossing gap opens between the outer- and inner-BQP bands, which we attribute primarily to interlayer single-particle hopping with possible contributions from interlayer Cooper pairing. We find that the $$d$$-wave superconducting gap of both BQP bands smoothly develops with momentum without abrupt jump in contrast to a previous ARPES study. Hybridization between the BQPs also gradually increases in going from the off-nodal to the anti-nodal region, which is explained by the momentum-dependence of the interlayer single-particle hopping. As possible mechanisms for the enhancement of the superconducting transition temperature, the hybridization between the BQPs, as well as the combination of phonon modes of the triple CuO$$_2$$ layers and spin fluctuations are discussed.

論文

Practical tests of neutron transmission imaging with a superconducting kinetic-inductance sensor

Vu, TheDang; 宍戸 寛明*; 相澤 一也; 小嶋 健児*; 小山 富男*; 及川 健一; 原田 正英; 奥 隆之; 曽山 和彦; 宮嶋 茂之*; et al.

Nuclear Instruments and Methods in Physics Research A, 1006, p.165411_1 - 165411_8, 2021/08

 被引用回数:1 パーセンタイル:15.62(Instruments & Instrumentation)

We found that the sizes of the Gd islands determined from the transmission image correlated strongly with those determined from the SEM image. We demonstrated the CB-KID could be used to identify (1) tiny voids in a thermally sprayed continuous Gd$$_2$$O$$_3$$ film in and (2) various mosaic morphologies and different eutectic microstructures in Wood's metal samples. The fact that the CB-KID system could be used to identify features of samples with a wide distribution of sizes and thicknesses is promising for real application of the device for imaging samples of interest to material scientists. Operating the CB-KID at higher temperatures appreciably improved the efficiency for simultaneously identifying the X and Y positions of hotspots. We also compared the detection efficiency with the PHITS simulations. We now plan to improve the detection efficiency by increasing the thickness of the $$^{10}$$B neutron conversion layer

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:22 パーセンタイル:86.67(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.

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