研究者詳細 - 笠原　成

論文 - 笠原　成

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Specific heat of Li-2(Pd(1-x)pt(x))(3)B superconductors [x=0, 0.5, and 1] 査読

Hiroyuki Takeya, Shigeru Kasahara, Mohammed El Massalami, Takashi Mochikua, Kazuto Hirata, Kazumasa Togano

PHYSICA B-CONDENSED MATTER 403 ( 5-9 ) 1078 - 1080 2008年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

The specific heat of Li-2(Pd1-xPtx)(3)B [x = 0, 0.5, 1] was measured. The heat jumps due to the superconducting transition were observed at 7.0, 3.9, and 2.5 K (T-c), respectively. These compounds have the same cubic structure (P4(3) 32) without mirror or inversion symmetry. Being noncentrosymmetric, it is interesting then to study the symmetry of superconducting gap function and Cooper pairs. The behavior of the electronic-specific heat C-es of Li-2(Pd1-xPtx)(3)B at low temperatures <T-c/3 showed different features with varying x. The temperature dependence of C,, for one end member, Li2Pd3B, follows an exponential behavior as in conventional superconductors, while that of Li2Pd1.5Pt1.5B and Li2Pt3B tends to follow a quadratic term rather than an exponential one. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.249

Superconductivity in the ternary intermetallics of La(3)Ni(4)X(4) (X = Si and Ge) 査読

H. Fujii, S. Kasahara

JOURNAL OF PHYSICS-CONDENSED MATTER 20 ( 7 ) 2008年2月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

Superconductivity in the ternary intermetallics of La(3)Ni(4)X(4) (X = Si and Ge) with the combination of AlB(2) and BaAl(4) layers is reported. Both compounds are type II superconductors with critical temperatures (T(c)) of 1.0 and 0.70 K for X = Si and Ge, respectively. The lower and the upper critical fields (H(c1)(0) and H(c2)(0)) for X = Si are 107 Oe and 16.5 kOe, whereas those for X = Ge are 68 Oe and 2.6 kOe, respectively. The gradient -dH(c2)/dT of La(3)Ni(4)Si(4) is extraordinarily higher than those of the other three analogues of La(3)Ni(4)Ge(4) and La(3)Pd(4)X(4). The magnetic penetration depth (lambda(0)) of 202 nm and Ginzburg-Landau coherence length (xi(0)) of 14 nm are derived for X = Si, while they are 206 and 36 nm for X = Ge.

DOI： 10.1088/0953-8984/20/7/075202

Superconducting Double Transition in PrOs4Sb12 Probed by Local Magnetization Measurements and Magneto-Optical Imaging 査読

Shigeru Kasahara, Kazuto Hirata, Hiroyuki Takeya, Tsuyoshi Tamegai, Hitoshi Sugawara, Daisuke Kikuchi, Hideyuki Sato

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 327 - 329 2008年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PHYSICAL SOC JAPAN

Double superconducting transition in PrOs4Sb12 has been studied carefully by performing the local magnetization measurements using micro-Hall probe and the magneto-optical imaging. Local magnetization curves for each element of the Hall probe reveal that there exists a significant difference in the transition temperature at each point; two phases which give different T-c's are stabilized in the crystal. Magneto-optical imaging at T < T-c2 and T-c2 < T < T-c1 also reveals a non-uniform superconducting nature. The characteristics of superconducting double transition in PrOs4Sb12 are discussed based on the local field inductions at multi-points.

DOI： 10.1143/JPSJS.77SA.327

Specific heat of lithium ternary borides under magnetic field 査読

Hiroyuki Takeya, Shigeru Kasahara, Mohammed El Massalami, Kazuto Hirata, Kazumasa Togano

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 463 111 - 114 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Superconductivity in Li2Pd3B and Li2Pt3B was confirmed at 7.0 K and 2.6 K, respectively. It is clear that their superconductivity is induced by Li addition. Their specific heat was measured under magnetic field by a heat-pulse relaxation method. Those materials have the same cubic structure (P4(3)32) composed of distorted octahedrons, whose corners are occupied by Pd/Pt. This structure does not have mirror or inversion symmetry along any directions. Those compounds are very interesting in relation to the symmetry of superconductivity. Sommerfeld (gamma T) and Debye (beta T-3) terms of Li2Pd3B were given as gamma = 8.3 mJ mol(-1) K-2 and beta = 1.4 mJ mol(-1) K-1. The Debye temperature is theta(D) = 202 K. The value of Delta C/gamma T at T-c was calculated to be 2.1. In the same manner, those parameters were described for Li2Pt3B as gamma = 9.6 mJ mol(-1) K-2, beta = 0.85 mJ mol(-1) K-1, theta(D) = 240 K, and Delta C/gamma T-c = 0.75. The superconducting state at zero magnetic field and the normal state achieved after quenching the superconductivity over H-c2 were compared and analyzed to understand the feature of those materials. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2007.05.015

Positive local magnetization in the superconducting state of PrOs4Sb12 査読

Shigeru Kasahara, Kazuto Hirata, Tsuyoshi Tamegai, Hitoshi Sugawara, Daisuke Kikuchi, Hideyuki Sato

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 463 71 - 75 2007年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Local magnetization measurements were performed by micro Hall-probe technique in the superconducting state of PrOs4Sb12, in which the time-reversal symmetry is broken. We have observed positive, i.e. ferromagnetic like, local magnetic induction just below the superconducting transition temperature, which changes into a usual Meissner signal as temperature goes down. The signal is dependent on the measuring points of the sample surface, and may be interpreted as a sign of the dilute magnetic moment arising from spontaneous current in the superconducting state. The characteristics of the superconductivity in PrOs4Sb12 including the presence of possible spontaneous magnetization is discussed based on the local magnetization measurements. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2007.05.004

Double transition in PrOs4Sb12 probed by local magnetization measurements using Hall probe array 査読

Shigeru Kasahara, Kazuto Hirata, Tsuyoshi Tamegai, Hitoshi Sugawara, Daisuke Kikuchi, Hideyuki Sato

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460 696 - 697 2007年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Double superconducting transition in PrOs4Sb12 has been studied carefully by local magnetization measurements using Hall probe array. Local magnetization curves for each element of the Hall probe reveal that there exists a significant difference in the transition temperature at each point; two phases which give different T-c are stabilized in the crystal. The characteristics of superconducting double transition in PrOs4Sb12 are discussed based on the local magnetization measurements at multi-points. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2007.03.134

Specific-heat studies of the spin-orbit interaction in noncentrosymmetric Li-2(Pd1-xPtx)(3)B (x=0,0.5,1) superconductors 査読

H. Takeya, M. ElMassalami, S. Kasahara, K. Hirata

PHYSICAL REVIEW B 76 ( 10 ) 2007年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

The temperature- and field-dependent specific heat C(T,H) measurement on the noncentrosymmetric superconductors Li2Pd3B, Li2Pt3B, and Li-2(Pd0.5Pt0.5)(3)B were carried out over a wide range of T and H. C(T,H) of the limit compounds is found to be distinctly different: within the superconducting phase, the electronic specific heat of the Pd-based compound follows C-e(S)(T < T-c=6.95 K,0 T)=3 exp[-16.4/T] J/mol K while for the Pt-based compound C-e(S)(T < T-c=2.56 K,0 T)=alpha T-2 mJ/mol K, where alpha=7.3 mJ/mol K-3. An increase in H tends to reduce weakly the exponential argument and the coefficient of the quadratic term. The above-mentioned findings are in agreement with the description that, due to the difference in the strength of the spin-orbit coupling, the pairing symmetry in the Pd- (Pt-) based compound is predominately a spin-singlet (spin-triplet) state. Within the very low-temperature range, the field-induced normal-state of the Pd-based limit manifests C-N(T,7T>H-c2)=9.3T+1.1T(3) mJ/mol K while that of the Pt-based isomorph shows C-N(T,7T>H-c2)=9.3T+0.92T(3) mJ/mol K. For the intermediate alloy Li-2(Pt0.5Pd0.5)(3)B, C(T,H) mimics that of the Pt-based compound; specifically, C-e(S)(T < T-c=3.9 K,0 T)=alpha T-2 mJ/mol K where alpha=4.6(2) mJ/mol K-3. The ratio of the coefficients of the quadratic terms in Li-2(Pt0.5Pd0.5)(3)B and Li2Pt3B, alpha Pd-Pt0.5(0.5)/alpha(Pt), is equal to Z(Pt0.5)Pd(0.5)(2)/Z(Pt)(2), confirming that the line nodes are driven by the spin-orbit interaction. The finding that these nodes can survive even in a 50% Pd-diluted material gives extra support to the reported claim that the x-dependent evolution of T-c, H-c1, H-c2, and (partial derivative H-c2/partial derivative T)(Tc) is almost linear.

DOI： 10.1103/PhysRevB.76.104506

Pressure effect and superconducting properties of lithium ternary borides 査読

Hiroyuki Takeya, Mohammed El Massalami, Kazuto Hirata, Takashi Mochiku, Shigeru Kasahara, Kazumasa Togano

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460 89 - 90 2007年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Li2Pd3B and Li2Pt3B show superconducting transition at the temperatures, 7.4 K and 2.6 K, respectively. These materials have the same cubic structure (P4(3)32) composed of distorted octahedrons, whose corners are occupied by Pd/Pt. This structure does not have mirror or inversion symmetry along any directions. It is a very interesting feature of those materials in relation to the symmetry of superconductivity. The samples were prepared by a two-stage arc-melting method. Their superconductivity is induced by Li addition. Controlling the Li stoichiometry is a key to synthesize high quality samples in the preparation process of arc-melting because Li is volatile at high temperatures. The specific heat measurements were carried out by heat-pulse relaxation and semi-adiabatic methods. Pressure effect was measured with a SQUID magnetometer using a low temperature hydrostatic micropressure cell at pressures up to around 1 GPa. The superconducting transition temperatures of both Li2Pd3B and Li2Pt3B decreased linearly with pressure. The pressure dependence, dT(c)/dP, were 0.091 and 0.090 K/GPa, respectively, (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2007.03.162

Comparison of CDR3 length among thymocyte subpopulations: Impacts of MHC and BV segment on the CDR3 shortening 査読

Matsutani Takaji, Ohmori Takehiko, Ogata Masaki, Soga Hiroyuki, Kasahara Shigeru, Yoshioka Takeshi, Suzuki Ryuji, Itoh Tsunetoshi

MOLECULAR IMMUNOLOGY 44 ( 9 ) 2378 - 2387 2007年3月

Physical properties of Li2Pd3B and Li2Pt3B superconductors 査読

Hiroyuki Takeya, Shigeru Kasahara, Mohammed El Massalami, Takashi Mochiku, Kazuto Hirata, Kazumasa Togano

PRICM 6: SIXTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, PTS 1-3 561-565 2079 - + 2007年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：TRANS TECH PUBLICATIONS LTD

Superconductivity in two Li-containing compounds of Li2Pd3B and Li2Pt3B was recently discovered. These materials, showing the superconducting transition at 7.2 K and 2.6 K, respectively, have the same cubic structure (P4(3)32) composed of distorted octahedrons without mirror or inversion symmetry along any directions. This is a very interesting feature of those materials in relation to the symmetry of superconductivity. Resistivity measurements in magnetic fields gave their upper critical fields, H-c2(0) = 45 kOe and 19 kOe, respectively. Their specific heat was measured using a heat-pulse relaxation method. The Sommerfeld coefficient (gamma) and Debye temperature (theta(D)) terms of Li2Pd3B were given as gamma=9.5 mJmol(-1)K(-2) and theta(D)=228 K. The value of Delta C/gamma T at T-c was calculated to be 1.7. In the same manner, those parameters were described for Li2Pt3B as gamma=9.6 mJmol(-1)K(-1), theta(D)=240 K, and Delta C/gamma T-c=0.75, respectively. Since Delta C/gamma T-c in the weak-coupling limit by the BCS theory is 1.43, the value of 1.7 for Li2Pd3B is slightly higher. The electronic specific heat of Li2Pd3B at a zero magnetic field follows the typical exponetial behavior discribed in the BCS theory, while that of Li2Pt3B shows quadratic behavior. This result suggests the line nodes exist in the superconducting gap of Li2Pt3B driven by the spin-orbit interaction.

DOI： 10.4028/www.scientific.net/MSF.561-565.2079

Physical properties of Li <inf>2</inf> Pd <inf>3</inf> B and Li <inf>2</inf> Pt <inf>3</inf> B superconductors

Takeya, H., Kasahara, S., El Massalami, M., Mochiku, T., Hirata, K., Togano, K.

Materials Science Forum 561-565 ( PART 3 ) 2007年

Local field measurements in PrOs4Sb12 with broken time-reversal symmetry 査読

Shigeru Kasahara, Tsuyoshi Tamegai, Hitoshi Sugawara, Hideyuki Sato

LOW TEMPERATURE PHYSICS, PTS A AND B 850 651 - + 2006年

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）出版者・発行元：AMER INST PHYSICS

We performed local magnetization measurements using micro-Hall probe in filled skutterudite PrOs4Sb12, which shows a superconducting state with broken time-reversal symmetry. It turns out that there appears a remarkable dip in the local magnetization hysteresis near zero field, which is characteristic of chiral superconductors, while temperature dependence of local magnetization shows no distinctive anomaly related to the spontaneous field. Possible situations of the spontaneous field is discussed from the results of local magnetization.

DOI： 10.1063/1.2354878

Comparative study of anisotropic superconductivity in CaAlSi and CaGaSi 査読

T Tamegai, K Uozato, S Kasahara, T Nakagawa, M Tokunaga

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 426 ( I ) 208 - 212 2005年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

In order to get some insight into the origin of the anomalous angular dependence of H-c2 in a layered intermetallic compound CaAlSi, electronic, superconducting, and structural properties are compared between CaAlSi and CaGaSi. The angular dependence of H-c2 in CaGaSi is well described by the anisotropic GL model. Parallel to this finding, the pronounced lattice modulation accompanying the superstructure along the e-axis in CaAlSi is absent in CaGaSi. A relatively large specific heat jump at the superconducting transition in CaAlSi compared with CaGaSi indicates the presence of strong electron-phonon coupling in CaAlSi, which may cause the superstructure and the anomalous angular dependence of H-c2. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2005.01.020

Peculiar superconductivity in PrOs4Sb12 probed by local magnetization 査読

S Kasahara, T Tamegai, H Sugawara, H Sato

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 426 ( I ) 381 - 385 2005年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We performed local magnetization measurements in the superconducting state of PrOS4Sb12 Using micro-Hall probe. For a magnetic field applied along one of the principal axes, a remarkable dip structure in the magnetization hysteresis loop was observed close to zero local magnetic induction. The anomaly is most pronounced when the magnetic field is applied only in a certain axis of the crystal, and is not observed along other two axes. We believe that the anomaly close to zero induction is universal to the spin-triplet superconductors with broken time-reversal symmetry. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2005.02.050

Local magnetization anomalies and inhomogeneous vortex penetration in the crossing-lattices state of Bi2Sr2CaCu2O8+y 査読

S. Kasahara, Y. Tokunaga, N. Kameda, M. Tokunaga, T. Tamegai

Physical Review B - Condensed Matter and Materials Physics 71 ( 22 ) 2005年6月

記述言語：英語掲載種別：研究論文（学術雑誌）

Nature of vortices in a highly anisotropic superconductor Bi2Sr2CaCu2O8+y is investigated in the presence of largely tilted magnetic fields. Direct visualizations of vortex distributions were performed under large in-plane fields up to 4000Oe by magneto-optical imaging technique. Our visualization clearly revealed inhomogeneous evolutions of the vortex penetration forming one-dimensional stripes. Comparative studies on the local magnetization revealed the existence of novel multiple peak structures in hysteresis loops. These peaks appear only in the increasing branch of the hysteresis curves when a magnetic field is applied nearly parallel to the superconducting plane. The origin of the novel anomalies is discussed on the basis of inhomogeneous vortex distribution. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.224505

Local magnetization anomalies and inhomogeneous vortex penetration in the crossing-lattices state of Bi2Sr2CaCu2O8+y 査読

S Kasahara, Y Tokunaga, N Kameda, M Tokunaga, T Tamegai

PHYSICAL REVIEW B 71 ( 22 ) 2005年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

Nature of vortices in a highly anisotropic superconductor Bi2Sr2CaCu2O8+y is investigated in the presence of largely tilted magnetic fields. Direct visualizations of vortex distributions were performed under large in-plane fields up to 4000 Oe by magneto-optical imaging technique. Our visualization clearly revealed inhomogeneous evolutions of the vortex penetration forming one-dimensional stripes. Comparative studies on the local magnetization revealed the existence of novel multiple peak structures in hysteresis loops. These peaks appear only in the increasing branch of the hysteresis curves when a magnetic field is applied nearly parallel to the superconducting plane. The origin of the novel anomalies is discussed on the basis of inhomogeneous vortex distribution.

DOI： 10.1103/PhysRevB.71.224505

Doping dependence of crossing vortex lattice in Bi2Sr2CaCu2O8+y 査読

S Kasahara, N Kameda, M Tokunaga, T Tamegai

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 412 ( SPEC. ISS. ) 440 - 443 2004年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Local magnetization hysteresis is studied in a highly anisotropic superconductor Bi2Sr2CaCu2O8+y under tilted magnetic fields using a micro Hall probe. At moderately high temperatures, we found novel multiple peak structures in the local magnetization hysteresis curves. These peaks appear only in the increasing branch of hysteresis curves when a magnetic field is applied nearly parallel to the superconducting plane. Possible origins of the novel peak structures are discussed on the basis of the evolution of the peaks with temperature. (C) 2004 Published by Elsevier B.V.

DOI： 10.1016/j.physc.2004.01.067

Pinning anomalies in organic layered superconductor kappa-(BEDT-TTF)(2)X {X = Cu(NCS)(2), Cu[N(CN)(2)]Br} 査読

S Kasahara, F Tateishi, H Caneko, T Hara, Y Nishio, K Kajita

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 388 607 - 608 2003年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

Vortices in organic superconductor kappa-(BEDT-TTF)(2)X {X = Cu(NCS)(2), Cu[N(CN)(2)]Br} are interesting for their anisotropic character. To investigate their dynamical behavior, ac complex susceptibility and dc electrical resistance measurements were done in the presence of vortices introduced by dc magnetic fields. In the course of experiments, we found that the dc field dependence of complex susceptibility changes drastically for moderate ac magnetic fields, i.e. the shielding effect of the system (-chi') has a peak structure and the dissipation term (chi") shows a dip. In addition to the anomalies in the susceptibility, it turned out that the electrical resistance has a dip structure under the same de magnetic fields. These anomalies imply that the vortices are less mobile there. (C) 2003 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4534(02)02763-6

Resistance oscillation and dynamical instabilities of vortices in kappa-(BEDT-TTF)(2)Cu(NCS)(2) 査読

S Kasahara, F Tateishi, H Caneko, T Hara, Y Nishio, K Kajita

SYNTHETIC METALS 137 ( 1-3 ) 1283 - 1284 2003年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE SA

We investigated dynamical properties of vortices in the organic superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2) through resistance measurements. In the course of experiments, we found time dependent resistance oscillations with periods of 10-100sec. It indicates that the vortex system undergoes the alternating change in the state between a highly mobile state and less mobile state. This oscillation was found to appear in a wide region of the magnetic field and in a narrow region of the electric current that drives vortices.

DOI： 10.1016/S0379-6779(02)01141-4

Dynamical behavior of vortices introduced into a layered superconductor κ-(BEDT-TTF)2Cu(NCS)2 査読

Shigeru Kasahara, Yutaka Nishio, Koji Kajita

Synthetic Metals 120 ( 1-3 ) 937 - 938 2001年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Vortices penetrating κ-(BEDT-TTF)2Cu(NCS)2 are interesting for its strongly two dimensional character. We investigated the behavior of vortices introduced by a dc-magnetic field through the shielding effect of the ac-magnetic field. For moderately strong ac-fields, we found an anomalous peak in the dc-field dependence of the shielding effect. The temperature dependence of the peak position is expressed as Hp = H0(Tc/T - 1). It turned out that the peak appears at the dc-field where the effective pinning potential on vortices has its maximum. We have confirmed this by estimating the pinning potential from the relaxation of the shielding, effect, which is caused by thermal creep of vortices and depends logarithmically on time.

DOI： 10.1016/S0379-6779(00)01155-3

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