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論文

Evidence for weak spin-orbit interaction experienced by Cooper pairs in the spin-triplet superconductor UPt$$_3$$; $$^{195}$$Pt-NMR study

青山 泰介*; 小手川 恒*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦*; 藤 秀樹*

Journal of the Physical Society of Japan, 88(6), p.064706_1 - 064706_7, 2019/06

$$^{195}$$Pt-NMR measurements under magnetic field ($$H$$) parallel to the $$c$$-axis in the vicinity of the upper critical field $$H_{rm c2}$$ have been carried out on the heavy-fermion superconductor UPt$$_3$$. The quasiparticle spin susceptibility was obtained from the measurements. The field dependence of the susceptibility suggests that the $$d$$-vector freely rotates in magnetic field. It is therefore concluded that spin-orbit interaction, which confines the direction of the $$d$$-vector with respect to the crystal axis, is weak in UPt$$_3$$.

論文

Vortex rectenna powered by environmental fluctuations

Lustikova, J.*; 塩見 雄毅*; 横井 直人*; 壁谷 典幸*; 木村 憲彰*; 家永 紘一郎*; 金子 真一*; 大熊 哲*; 高橋 三郎*; 齊藤 英治

Nature Communications (Internet), 9, p.4922_1 - 4922_6, 2018/11

 被引用回数:1 パーセンタイル:49.95(Multidisciplinary Sciences)

A rectenna, standing for a rectifying antenna, is an apparatus which generates d.c. electricity from electric fluctuations. It is expected to realize wireless power transmission as well as energy harvesting from environmental radio waves. To realize such rectification, devices that are made up of internal atomic asymmetry such as an asymmetric junction have been necessary so far. Here we report a material that spontaneously generates electricity by rectifying environmental fluctuations without using atomic asymmetry. The sample is a common superconductor without lowered crystalline symmetry, but, just by putting it in an asymmetric magnetic environment, it turns into a rectifier and starts generating electricity. Superconducting vortex strings only annihilate and nucleate at surfaces, and this allows the bulk electrons to feel surface fluctuations in an asymmetric environment: a vortex rectenna. The rectification and generation can be switched on and off with only a slight change in temperature or external magnetic fields.

論文

Fermi surface of ThRu$$_{2}$$Si$$_{2}$$ as a reference to the strongly correlated isostructural metals investigated by quantum oscillations

松本 裕司*; 芳賀 芳範; 立岩 尚之; 青木 晴善*; 木村 憲彰*; 山村 朝雄*; 山本 悦嗣; 松田 達磨*; Fisk, Z.*; 山上 浩志*

Journal of the Physical Society of Japan, 85(10), p.104709_1 - 104709_7, 2016/10

 被引用回数:2 パーセンタイル:63.85(Physics, Multidisciplinary)

dHvA oscillations were detected on an actinide compound ThRu$$_2$$Si$$_2$$ which is regarded as a reference to strongly correlated electron systems URu$$_2$$Si$$_2$$ and CeRu$$_2$$Si$$_2$$. Observed Fermi surfaces well coincides with the band structure calculations, as well as experimentally obtained ones for a heavy fermion compound CeRu$$_2$$Si$$_2$$. On the other hand, Fermi surfaces of URu$$_2$$Si$$_2$$ have significantly different characteristics, suggesting an itinerant ground state of 5f electrons.

論文

Unusual pressure evolution of the Meissner and Josephson effects in the heavy-fermion superconductor UPt$$_3$$

郷地 順*; 住山 昭彦*; 山口 明*; 本山 岳*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦

Physical Review B, 93(17), p.174514_1 - 174514_5, 2016/05

 被引用回数:1 パーセンタイル:88.02(Materials Science, Multidisciplinary)

The Josephson effect between a single crystal UPt$$_3$$ and a conventional superconductor Al has been investigated under pressure. A possible change of the superconducting order parameter has been detected at a critical $$P_c$$ where the symmetry-breaking antiferromagnetic order disappears. The conclusion is also supported by the different behaviors observed in Josephson current and penetration depth.

論文

Enhancement of the cyclotron effective mass in U$$_{0.03}$$Th$$_{0.97}$$Ru$$_2$$Si$$_2$$

芳賀 芳範; 松本 裕司*; 立岩 尚之; 山本 悦嗣; 木村 憲彰*; 山村 朝雄*; Fisk, Z.

Journal of Physics; Conference Series, 592(1), p.012036_1 - 012036_5, 2015/03

 被引用回数:2 パーセンタイル:24.39

We investigate the modification of the electronic state of ThRu$$_2$$Si$$_2$$ upon replacing non magnetic Th by U. We successfully observed the quantum oscillation signals from the Fermi surface. The observed Fermi surfaces did not show a significant change in size for the U$$_{0.03}$$Th$$_{0.97}$$Ru$$_2$$Si$$_2$$ sample. However the enhancement of the cyclotron effective mass demonstrates the hybridization of the 5$$f$$ states with the conduction bands.

論文

Electronic states in antiferromagnetic compound URhIn$$_5$$ investigated by de Haas-van Alphen effect and high pressure resistivity measurements

松本 裕司; 芳賀 芳範; 立岩 尚之; 山本 悦嗣; 木村 憲彰*; 青木 晴善*; Fisk, Z.

JPS Conference Proceedings (Internet), 3, p.011097_1 - 011097_5, 2014/06

Single crystal samples of a new uranium compound URhIn$$_5$$ with the well-known tetragonal HoCoGa$$_5$$-type structure have been grown by the indium flux method. Although this compound is isostructural to a Ga-analogue URhGa$$_5$$, the unit cell volume is significantly larger in URhIn$$_5$$. In contrast to non-magnetic behavior in the isostructural URhGa$$_5$$, URhIn$$_5$$ has a magnetic ground state with a magnetic transition at 98 K, indicating a drastic difference in electronic states between these compounds.

論文

Single-crystal growth and de Haas-van Alphen effect study of ThRu$$_2$$Si$$_2$$

松本 裕司*; 芳賀 芳範; 立岩 尚之; 青木 晴善*; 木村 憲彰*; 松田 達磨*; 山本 悦嗣; Fisk, Z.; 山上 浩志*

JPS Conference Proceedings (Internet), 3, p.011096_1 - 011096_5, 2014/06

Electronic differences between heavy Fermion CeRu$$_2$$Si$$_2$$ and isoelectronic nonmagnetic ThRu$$_2$$Si$$_2$$ have been investigated. We succeeded in observing the de Haas-van Alphen oscillation in a high quality single crystal of ThRu$$_2$$Si$$_2$$. The mean free path of conduction carriers has been estimated as 6400 ${AA}$, indicating the high quality of the present sample.

論文

Josephson effect between UPt$$_3$$ and conventional superconductors under pressure

郷地 順*; 住山 昭彦*; 山口 明*; 本山 岳*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦

JPS Conference Proceedings (Internet), 3, p.011067_1 - 011067_6, 2014/06

The Josephson critical current $$I_{rm c}$$ between a single crystal UPt$$_3$$ and conventional superconductors has been measured under pressure. The observation of $$I_{rm c}$$ well above the critical pressure 0.25 GPa, together with a Fraunhofer-like pattern in the magnetic field modulation of $$I_{rm c}$$ indicates that the Josephson effect is allowed in the superconducting state of UPt$$_3$$.

論文

Pairing symmetry of UPt$$_3$$ probed by thermal transport tensors

井澤 公一*; 町田 洋*; 伊藤 淳史*; 宗 義尚*; 多田 勝哉*; 芳賀 芳範; 山本 悦嗣; 木村 憲彰*; 大貫 惇睦; 堤 康雅*; et al.

Journal of the Physical Society of Japan, 83(6), p.061013_1 - 061013_8, 2014/06

 被引用回数:15 パーセンタイル:21.56(Physics, Multidisciplinary)

Recent advances on the study of the gap symmetry in UPt$$_3$$ by thermal conductivity tensors are reported. The field-angle-resolved thermal conductivity shows spontaneous twofold symmetry breaking i the gap function for the high-field C-phase, indicating the pairing symmetry of UPt$$_3$$ belongs to an $$E_{1u}$$ representation in the $$f$$-wave category.

論文

Anomalous field-angle dependence of the specific heat of heavy-fermion superconductor UPt$$_3$$

橘高 俊一郎*; 安 幸治*; 榊原 俊郎*; 芳賀 芳範; 山本 悦嗣; 木村 憲彰*; 大貫 惇睦; 町田 一成*

Journal of the Physical Society of Japan, 82(2), p.024707_1 - 024707_5, 2013/02

 被引用回数:9 パーセンタイル:36.52(Physics, Multidisciplinary)

The field-angle variation of the specific heat of the heavy-fermion superconductor UPt$$_3$$ at low temperatures down to 50 mK was investigated. The data show that the unusual upper critical field becomes marked only when the magnetic field is pointed close to the $$c$$-axis. However, the attempt to observe the superconducting gap structure through field-angle dependence of the specific heat failed, because of the small anisotropy compared to the experimental accuracy of 0.5%. It implies that the field-induced excitation of the heavy quasiparticles occur isotropically with respect to the angle.

論文

Delocalization of the $$f$$ electron in Ce$$_x$$La$$_{1-x}$$Ru$$_2$$Si$$_2$$; The de Haas-van Alphen effect measurement

松本 裕司; 木村 憲彰*; 小松原 武美*; 青木 晴善*; 栗田 伸之*; 寺嶋 太一*; 宇治 進也*

Journal of Physics; Conference Series, 391, p.012042_1 - 012042_4, 2012/12

 被引用回数:1 パーセンタイル:47.35

CeRu$$_2$$Si$$_2$$は、$$gamma$$ of 350mJ/mol K$$^2$$を持つ典型的な重い電子系物質である。この物質の[001]方向に磁場を印加したときに、7.7Tでメタ磁性転移を引き起こす。一方、この(001)面内に磁場を印加したときは、メタ磁性を引き起こさない。この大きな磁気異方性は、CeをLaに置換したときにおいても、常に残っている。CeをLaに置換すると、$$x_c$$=0.91で反強磁性秩序を起こし、Ceが希薄濃度になると反強磁性秩序は消失する。そして、Ce濃度が非常に薄い濃度領域で不純物近藤効果を引き起こす。$$x$$=0.02の試料では、近藤温度を1.3Kと見積もった。その濃度において、dHvA振動の観測に成功した。そして、温度に対してフェルミ面が連続的に変化していることを明らかにした。このことは、f電子は、不純物近藤効果を起こし近藤シングレットを形成したときは遍歴していて、温度の上昇とともに局在化していくことを示している。

論文

Measurement of the Josephson effect of heavy-fermion superconductor UPt$$_3$$ as a test of the odd-parity order parameter

郷地 順*; 住山 昭彦*; 本山 岳*; 山口 明*; 木村 憲彰*; 山本 悦嗣; 芳賀 芳範; 大貫 惇睦

Journal of the Physical Society of Japan, 81(11), p.113701_1 - 113701_4, 2012/11

 被引用回数:5 パーセンタイル:54.14(Physics, Multidisciplinary)

The Josephson critical current I$$_c$$ between a single-crystal UPt$$_3$$ and Al has been measured for the junctions on the UPt$$_3$$ surface perpendicular to the hexagonal axes. The obtained results contradict the $$E_{2u}$$ scenario for the odd-parity order parameter in UPt$$_3$$, in which the Josephson effect is forbidden in the three directions, whereas the recently proposed $$E_{1u}$$ scenario permits, at least, the $$a$$- and $$c$$-axis Josephson couplings.

論文

Magnetic behavior near the boundary of 4$$f$$ delocalization in ferromagnetic CeRu$$_2$$Ge$$_2$$ and paramagnetic CeRu$$_2$$Si$$_2$$ observed by Ce $$M_{4,5}$$ XAS and XMCD

岡根 哲夫; 竹田 幸治; 山上 浩志; 藤森 淳; 松本 裕司; 木村 憲彰*; 小松原 武美*; 青木 晴善*

Physical Review B, 86(12), p.125138_1 - 125138_11, 2012/09

 被引用回数:7 パーセンタイル:58.92(Materials Science, Multidisciplinary)

X-ray absorption (XAS) and its magnetic circular dichroism (XMCD) were measured at the Ce $$M_{4,5}$$ absorption edges of ferromagnetic CeRu$$_2$$Ge$$_2$$ and paramagnetic CeRu$$_2$$Si$$_2$$: both compounds are considered to be located near the boundary of delocalization of Ce 4$$f$$ electrons. While the XAS line shape varies clearly reflecting the variation in the 4$$f$$ delocalization, the line-shape variation in XMCD is hardly discernible under various conditions of temperature and magnetic field. The XAS line-shape variation can be explained as effects of the variations in the 4$$f$$ occupation number and in the ratio of $$J$$ = 7/2 states in the ground states, both of which are closely related to the 4$$f$$ delocalization. The 4$$f$$ delocalization also causes a decrease in the ratio of the orbital magnetic moment to the spin magnetic moment. The magnetic-field dependence of XAS suggests that the Ce 4$$f$$ electrons retain a delocalized character across the metamagnetic transition in CeRu$$_2$$Si$$_2$$.

論文

Twofold spontaneous symmetry breaking in the heavy-fermion superconductor UPt$$_3$$

町田 洋*; 伊藤 淳史*; 宗 義尚*; 井澤 公一*; 芳賀 芳範; 山本 悦嗣; 木村 憲彰*; 大貫 惇睦; 堤 康雅*; 町田 一成*

Physical Review Letters, 108(15), p.157002_1 - 157002_5, 2012/04

 被引用回数:55 パーセンタイル:7.1(Physics, Multidisciplinary)

The field-orientation dependent thermal conductivity of the heavy-fermion superconductor UPt$$_3$$ was measured down to very low temperatures and under magnetic fields throughout the distinct superconducting phases: $$B$$ and $$C$$ phases. In the $$C$$ phase, a striking twofold oscillation of the thermal conductivity within the basal plane is resolved reflecting the superconducting gap structure with a line of node along the $$a$$ axis. From this result together with the symmetry consideration, the gap function of UPt$$_3$$ is determined as a $$E_{1u}$$ representation characterized by a combination of two line nodes at the tropics and point nodes at the poles.

論文

Electronic structure of heavy fermion uranium compounds studied by core-level photoelectron spectroscopy

藤森 伸一; 大河内 拓雄*; 川崎 郁斗; 保井 晃; 竹田 幸治; 岡根 哲夫; 斎藤 祐児; 藤森 淳; 山上 浩志; 芳賀 芳範; et al.

Journal of the Physical Society of Japan, 81(1), p.014703_1 - 014703_9, 2012/01

 被引用回数:27 パーセンタイル:16.55(Physics, Multidisciplinary)

重い電子系化合物UGe$$_2$$, UCoGe, URhGe, URu$$_2$$Si$$_2$$, UNi$$_2$$Al$$_3$$, UPd$$_2$$Al$$_3$$, UPt$$_3$$及び典型的な遍歴・局在系に対して高分解能内殻光電子分光実験を行い、その電子状態に対する研究を行った。UGe$$_2$$, UCoGe, URhGe, URu$$_2$$Si$$_2$$, UNi$$_2$$Al$$_3$$の内殻スペクトルは遍歴的な化合物の内殻スペクトルに類似しており、これらの化合物ではU 5$$f$$電子はよく混成していることを示している。一方でUPd$$_2$$Al$$_3$$及びPt$$_3$$の内殻スペクトルはこれらのスペクトルとは異なっており、U 5$$f$$電子は電子相関効果が強いことを示している。

論文

Resonant angle-resolved photoelectron spectroscopy of substitutional solid solutions of CeRu$$_2$$Si$$_2$$

岡根 哲夫; 川崎 郁斗; 保井 晃; 大河内 拓雄*; 竹田 幸治; 藤森 伸一; 斎藤 祐児; 山上 浩志; 藤森 淳; 松本 裕司*; et al.

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA060_1 - SA060_3, 2011/07

 被引用回数:1 パーセンタイル:86.08(Physics, Multidisciplinary)

Angle-resolved photoelectron spectroscopy was measured in the Ce 3$$d$$$$rightarrow$$4$$f$$ resonance energy region for the paramagnetic state of CeRu$$_2$$Si$$_2$$, Ce$$_{0.84}$$La$$_{0.16}$$Ru$$_2$$Si$$_2$$ and LaRu$$_2$$Si$$_2$$ to investigate a variation of band structures around the quantum critical point (QCP). While the results clearly demonstrate the difference of the band structures between CeRu$$_2$$Si$$_2$$ and LaRu$$_2$$Si$$_2$$, the observed band structures of CeRu$$_2$$Si$$_2$$ and Ce$$_{0.84}$$La$$_{0.16}$$Ru$$_2$$Si$$_2$$ resemble each other. The results indicate that the Ce $$4f$$ electrons in the paramagnetic state have an itinerant character in either side of the critical composition, and Ce$$_{1-x}$$La$$_{x}$$Ru$$_2$$Si$$_2$$ near QCP is similar to CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$.

論文

Band structures of CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$ studied by resonant soft X-ray ARPES

岡根 哲夫; 大河内 拓雄*; 竹田 幸治; 藤森 伸一; 保井 晃; 斎藤 祐児; 山上 浩志; 藤森 淳; 松本 裕司*; 杉 基紀*; et al.

Physica Status Solidi (B), 247(3), p.397 - 399, 2010/03

Angle-resolved photoelectron spectroscopy measurements were made in the Ce $$3d$$$$rightarrow$$4$$f$$ resonance energy region for the paramagnetic state of CeRu$$_2$$Si$$_2$$, CeRu$$_2$$(Si$$_{0.82}$$Ge$$_{0.18}$$)$$_2$$ and LaRu$$_2$$Si$$_2$$ to investigate a variation of band structures around the quantum critical point. The results indicate that the Ce $$4f$$ electrons in the paramagnetic state have an itinerant character and participate in the formation of energy bands both in CeRu$$_2$$Si$$_2$$ and CeRu$$_2$$(Si$$_{0.82}$$Ge$$_{0.18}$$)$$_2$$, and the change of the band structures in the paramagnetic states should be continuous around the quantum critical point of the CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$ system.

論文

4$$f$$-derived Fermi surfaces of CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$ near the quantum critical point; Resonant soft-X-ray ARPES study

岡根 哲夫; 大河内 拓雄*; 竹田 幸治; 藤森 伸一; 保井 晃; 斎藤 祐児; 山上 浩志; 藤森 淳; 松本 裕司*; 杉 基紀*; et al.

Physical Review Letters, 102(21), p.216401_1 - 216401_4, 2009/05

 被引用回数:21 パーセンタイル:23.34(Physics, Multidisciplinary)

Angle-resolved photoelectron spectroscopy in the Ce $$3d$$$$rightarrow$$4$$f$$ excitation region was measured for the paramagnetic state of CeRu$$_2$$Si$$_2$$, CeRu$$_2$$(Si$$_{0.82}$$Ge$$_{0.18}$$)$$_2$$, and LaRu$$_2$$Si$$_2$$ to investigate the changes of the 4$$f$$ electron Fermi surfaces around the quantum critical point. While the difference of the Fermi surfaces between CeRu$$_2$$Si$$_2$$ and LaRu$$_2$$Si$$_2$$ was experimentally confirmed, a strong 4$$f$$-electron character was observed in the band structures and the Fermi surfaces of CeRu$$_2$$Si$$_2$$ and CeRu$$_2$$(Si$$_{0.82}$$Ge$$_{0.18}$$)$$_2$$, consequently indicating a delocalized nature of the 4$$f$$ electrons in both compounds. The absence of Fermi surface reconstruction across the critical composition suggests that SDW quantum criticality is more appropriate than local quantum criticality in CeRu$$_2$$(Si$$_{1-x}$$Ge$$_{x}$$)$$_2$$.

論文

Higher-order collinear interaction and magnetic excitation in the 5f localized system U$$_{3}$$Pd$$_{20}$$Si$$_{6}$$

目時 直人; 小池 良浩; 芳賀 芳範; 金子 耕士; 荒木 新吾; McEwen, K. A.*; 神木 正史*; 阿曽 尚文*; Lander, G. H.; 小松原 武美*; et al.

Journal of Physics; Condensed Matter, 15(28), p.S1957 - S1963, 2003/07

 被引用回数:2 パーセンタイル:82.87(Physics, Condensed Matter)

ウラン局在系U$$_{3}$$Pd$$_{20}$$Si$$_{6}$$の磁気構造,スピン波励起と結晶場励起、そして低エネルギーの励起について、報告する。この物質はウラン化合物としてはめずらしく局在的な5f電子状態を持つ。4aサイトと8cサイトのウランの高次の相互作用にともなう、磁気相図,コリニアーな磁気構造について議論する。さらに、磁気励起についても5f電子のへん歴・局在性の観点から議論する。

論文

Magnetic structure, phase diagram, and a new type of spin-flop transition dominated by higher order interaction in a localized 5$$f$$ system U$$_{3}$$Pd$$_{20}$$Si$$_{6}$$

小池 良浩; 目時 直人; 芳賀 芳範; McEwen, K. A.*; 神木 政史*; 山本 竜之介*; 阿曽 尚文*; 立岩 尚之*; 小松原 武美*; 木村 憲彰*; et al.

Physical Review Letters, 89(7), p.077202_1 - 077202_4, 2002/08

 被引用回数:6 パーセンタイル:54.03(Physics, Multidisciplinary)

局在5f電子系ウラン金属間化合物U$$_{3}$$Pd$$_{20}$$Si$$_{6}$$の磁気構造,磁気相図,新しい機構に基づくメタ磁性転移を、原研が開発した液体ヘリウムフリー中性子散乱実験用10Tマグネット及び希釈冷凍機を用いた中性子回折実験によって明らかにした。基底状態では4aサイトの強磁性秩序と8cサイトの反強磁性秩序状態が、ウランスピンが平行になるように結合していることが明らかになった。この物質におけるサイト間ハイゼンベルグ交換相互作用はキャンセルしている。そのため、この磁気構造が安定化するためには、より高次の相互作用が必要であることが明らかになった。その起源として最も可能性が高いのは、結晶構造及び磁気構造から4体の交換相互作用と考えられる。5f電子系においては4体相互作用はいまだかつて観察された報告例がなく、交換相互作用のキャンセルと、サイト間の結合に伴うフラストレーションによって生じた強い磁気揺らぎによって4体相互作用が顕著に現れたと結論できる。

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