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論文

Magnetic anisotropy and thermodynamic anomaly in the superconducting mixed state of UBe$$_{13}$$ probed by static dc magnetization measurements

清水 悠晴*; 芳賀 芳範; 柳澤 達也*; 網塚 浩*

Physical Review B, 93(2), p.024502_1 - 024502_8, 2016/01

 被引用回数:7 パーセンタイル:43.28(Materials Science, Multidisciplinary)

Static dc magnetization measurements were performed for a heavy fermion superconductor UBe$$_{13}$$ single crystal. For the fields along the [100] and [110] directions of cubic lattice, a magnetic anomaly was found at a characteristic field $$H_{rm Mag}^{*}$$ within the superconducting mixed state. It was also found that magnetic anisotropy became more significant above this field. The present study shows that the thermodynamic property of superconductivity changes as a function of magnetic field.

論文

Field-orientation dependence of low-energy quasiparticle excitations in the heavy-electron superconductor UBe$$_{13}$$

清水 悠晴*; 橘高 俊一郎*; 榊原 俊郎*; 芳賀 芳範; 山本 悦嗣; 網塚 浩*; 堤 康雅*; 町田 一成*

Physical Review Letters, 114(14), p.147002_1 - 147002_6, 2015/04

 被引用回数:24 パーセンタイル:11.92(Physics, Multidisciplinary)

Low-energy excitation in the superconducting state of UBe$$_{13}$$ were studied by means of specific-heat measurements in a rotating field. Quite unexpectedly, the magnetic-field dependence of specific heat is linear in field at low fields with an isotropic field-angle dependence. The observation implies that the gap is fully open over the Fermi surfaces, in contrast to the previous expectation.

論文

Valence state in Ce-based heavy fermion compounds at high magnetic fields

松田 康弘*; Her, J.-L.*; 道村 真司*; 稲見 俊哉; 海老原 孝雄*; 網塚 浩*

JPS Conference Proceedings (Internet), 3, p.011044_1 - 011044_6, 2014/06

CeRh$$_2$$Si$$_2$$の放射光X線吸収実験を32Tまでのパルス強磁場下で行った。Ceの価数は5Kで3+よりわずかに大きく、20T以上の磁場印加に伴い減少する。磁場誘起の価数変化は磁化過程のメタ磁性転移に対応している。この現象は我々の以前に行ったCeRu$$_2$$Si$$_2$$の結果に似ており、Ce系重い電子系化合物に共通の現象と思われる。

論文

DC magnetization study on heavy-electron superconductor UBe$$_{13}$$

清水 悠晴*; 芳賀 芳範; 柳澤 達也*; 網塚 浩*; 青木 大*; Brison, J.-P.*; Braithwaite, D.*

JPS Conference Proceedings (Internet), 3, p.015009_1 - 015009_6, 2014/06

Static DC magnetization measurements were performed in order to investigate magnetic response of the unconventional superconducting state of UBe$$_{13}$$. An unusual anomaly was observed inside the superconducting mixed state corresponding either to a peculiarity of superconducting diamagnetism or the anomalous vortex core structures.

論文

X-ray backscattering study of crystal lattice distortion in hidden order of URu$$_2$$Si$$_2$$

田端 千紘*; 稲見 俊哉; 道村 真司*; 横山 淳*; 日高 宏之*; 柳澤 達也*; 網塚 浩*

Philosophical Magazine, 94(32-33), p.3691 - 3701, 2014/00

 被引用回数:8 パーセンタイル:43.65(Materials Science, Multidisciplinary)

We performed synchrotron X-ray diffraction measurements on a small single crystal of URu$$_2$$Si$$_2$$. A backscattering diffraction setup (2$$thetasim179.81^circ$$) in combination with a Si(6 6 0) monochromator ensures a high instrumental resolution of $$Delta d/d sim 7.3 times 10^{-6}$$, where $$d$$ denotes a lattice-plane spacing and $$Delta d$$ is its spread expressed as the full width at half maximum (FWHM). We carefully measured the (5 5 0) Bragg peak in the temperature range between 5 and 25 K, and found it to show no signature of broadening and splitting when "Hidden Order (HO)" sets in below 17.5 K. Temperature variation of the peak position closely follows the behaviour of the known linear thermal expansion coefficient. Detailed analysis of the peak width reveals that the tetragonal fourfold rotational symmetry of URu$$_2$$Si$$_2$$ is conserved in HO within the experimental accuracy of the orthorhombicity of $$|b-a|/(b+a)leq3.0times10^{-5}$$.

論文

Observation of an unusual magnetic anomaly in the superconducting mixed state of heavy-fermion compound UBe$$_{13}$$ by precise dc magnetization measurements

清水 悠晴*; 芳賀 芳範; 池田 陽一*; 柳澤 達也*; 網塚 浩*

Physical Review Letters, 109(21), p.217001_1 - 217001_5, 2012/11

 被引用回数:15 パーセンタイル:29.11(Physics, Multidisciplinary)

Precise dc magnetization measurements were performed on a heavy fermion superconductor UBe$$_{13}$$. We observed a magnetic anomaly in the superconducting mixed state, implying an unusual superconducting state. The origin of the anomaly is discussed based on an unusual superconducting response or a peculiar normal-state magnetization at the vortex cores.

論文

Maki parameter and upper critical field of the heavy-fermion superconductor UBe$$_{13}$$

清水 悠晴*; 池田 陽一*; 若林 琢巳*; 芳賀 芳範; 天谷 健一*; 日高 宏之*; 柳澤 達也*; 網塚 浩*

Journal of the Physical Society of Japan, 80(9), p.093701_1 - 093701_4, 2011/09

 被引用回数:7 パーセンタイル:46.84(Physics, Multidisciplinary)

Low-temperature specific heat measurements under magnetic field were performed on a single crystal UBe$$_{13}$$. The specific heat shows a $$T^3$$ behavior below $$sim$$0.7 $$T$$$$_{rm c}$$, where $$T$$$$_{rm c}$$ is the superconducting transition temperature, suggesting the existence of point nodes in the superconducting gap. Together with the isotropic behavior of the upper critical magnetic field, the symmetry of the Cooper paring is discussed.

論文

Specific heat and magnetization studies of the superconducting mixed state of UBe$$_{13}$$

清水 悠晴*; 池田 陽一*; 若林 琢巳*; 天谷 健一*; 芳賀 芳範; 日高 宏之*; 柳澤 達也*; 網塚 浩*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA100_1 - SA100_3, 2011/07

 被引用回数:1 パーセンタイル:86.85(Physics, Multidisciplinary)

Low-temperature specific heat and static dc magnetization measurements have been performed in the superconducting state of the heavy-fermion compound UBe$$_{13}$$. The superconducting phase diagram was obtained from these measurements. We obtained Ginzburg-Landau parameter as a function of temperature and showed that a paramagnetic effect is present down to 0.5 K.

論文

Ultrasonic measurements on the cage-structured clathrate compound U$$_3$$Pd$$_{20}$$Si$$_6$$

柳澤 達也*; 立岩 尚之; 真山 太一*; 齋藤 旬*; 日高 宏之*; 網塚 浩*; 芳賀 芳範; 根本 祐一*; 後藤 輝孝*

Journal of the Physical Society of Japan, 80(Suppl.A), p.SA105_1 - SA105_3, 2011/07

 被引用回数:3 パーセンタイル:68.12(Physics, Multidisciplinary)

Ultrasonic measurements of U$$_3$$Pd$$_{20}$$Si$$_6$$ were performed in order to investigate elastic properties of the cage-structured compound U$$_3$$Pd$$_{20}$$Si$$_6$$. At temperatures over antiferromagnetic ordering at $$T_{rm N}$$ = 19 K, neither an up-turn anomaly nor frequency dependence of the elastic constants, regarding the ultrasonic dispersion (UD), was found. A drastic change of $$C_{44}$$ mode at $$T_{rm N}$$, in particular, implies a strong magneto-elastic coupling of 5$$f$$-electrons or a possible contribution of a ferroquadrupole interaction to the antiferromagnetism in U$$_3$$Pd$$_{20}$$Si$$_6$$.

論文

Magnetization in the superconducting mixed state of the heavy-fermion compound UBe$$_{13}$$

清水 悠晴*; 池田 陽一*; 若林 琢巳*; 天谷 健一*; 芳賀 芳範; 日高 宏之*; 柳澤 達也*; 網塚 浩*

Journal of Physics; Conference Series, 273, p.012084_1 - 012084_4, 2011/02

 被引用回数:3 パーセンタイル:29.3

Static dc magnetization measurements in the superconducting mixed state of a single crystal UBe$$_{13}$$ were performed by means of a capacitance Faraday-force method down to 0.24 K. Below the upper critical field $$B_{c2}$$, not only a peak effect but also an additional broad anomaly have been observed in magnetization curves. We report superconducting phase diagram of UBe$$_{13}$$ obtained by our magnetization measurements, including these anomalies.

論文

XMCD spectroscopy on valence fluctuating and heavy fermion compounds in very high magnetic fields up to 40 T

松田 康弘*; Her, J. L.*; 稲見 俊哉; 大和田 謙二; Ouyang, Z. W.*; 岡田 郷子*; 野尻 浩之*; 光田 暁弘*; 和田 裕文*; 吉村 一良*; et al.

Journal of Physics; Conference Series, 190, p.012019_1 - 012019_6, 2009/11

 被引用回数:7 パーセンタイル:11.52

$$L$$-edge X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) in several rare-earth elements have been studied in pulsed high magnetic fields up to 40 T. XMCD spectrum of Eu in EuNi$$_2$$(Si$$_{0.18}$$Ge$$_{0.82}$$)$$_2$$ shows a characteristic two peak structure, reflecting the valence fluctuation. However, in YbInCu$$_4$$, it is found that the XMCD spectrum of Yb shows only a single peak. In contrast to XMCD, two absorption bands in XAS are observed in both compounds. The intensity ratio between the two absorption bands changes significantly with increasing magnetic field in these materials, suggesting the field-induced valence change. The high magnetic field XMCD and XAS measurements have also been conducted in an antiferromagnetic heavy fermion compound CeRh$$_2$$Si$$_2$$. The Ce valence is found to be nearly trivalent and insensitive to magnetic field. The XMCD at Ce $$L$$$$_{2}$$-edge increases rapidly around 26 T corresponding to the metamagnetic transition.

論文

Magnetic, elastic, transport and fermi surface properties of a ferromagnetic compound UGa$$_{2}$$

本間 徹生; 山本 悦嗣; 芳賀 芳範; 摂待 力生*; 荒木 新吾*; 稲田 佳彦*; 竹内 徹也*; 桑原 慶太郎*; 網塚 浩*; 榊原 俊郎*; et al.

Physica B; Condensed Matter, 281-282, p.195 - 196, 2000/06

 被引用回数:2 パーセンタイル:82.33

われわれは六方晶AlB$$_{2}$$型結晶構造をもつ強磁性体UGa$$_{2}$$の5f電子状態を調べるために、磁気、弾性、伝導的特性とドハースファンアルフェン効果の実験を行った。これらの実験結果から六方晶の[0001]面内に100K以下で歪みが生じることを見いだした。これは、[1120]方向に向いた強磁性モーメントの発達によって引き起こされていると考えられる。

論文

UPt$$_{3}$$における奇パリティ超伝導状態

藤 秀樹*; 北岡 良雄*; 朝山 邦輔*; 榊原 俊郎*; 天谷 健一*; 池田 昌隆*; 田山 孝*; 網塚 浩*; 木村 憲彰*; 摂待 力生*; et al.

固体物理, 31(9), p.763 - 774, 1996/00

UPt$$_{3}$$は1984年の発見以来、10年以上注目を集め続けている。最大の特徴は磁場中で複数の超伝導相を有することであり、他の超伝導体には見られない特徴である。我々はUPt$$_{3}$$の単結晶を育成し、固相電解を施すことによって世界最高純度の試料を得ることに成功した。この単結晶を用いて核磁気共鳴(NMR)及び磁化による超伝導状態の研究を行った。その結果knight-shiftがBCS理論で予想されるものと異なった温度依存性を示すことが明らかとなった。このことは、Cooper対を形成する電子のスピンが平行であり、奇パリティ超伝導が実現していることを示す直接的な証拠である。

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