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Pd
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In close to a zero-temperature structural instabilityGruner, T.*; Lucas, S.*; Geibel, C.*; 金子 耕士; 筒井 智嗣*; Schmalzl, K.*; Stockert, O.*
Physical Review B, 106(11), p.115142_1 - 115142_6, 2022/09
被引用回数：1 パーセンタイル：17.38(Materials Science, Multidisciplinary)The disappearance of a charge-density-wave (CDW) transition in Lu(PtPd)In is thought to be closely linked to a maximum of the superconducting transition temperature in the system. We studied the superstructure and the phonon softening in Lu(Pt
Pd)In by means of neutron and high-resolution inelastic X-ray scattering. A full phonon softening at 
= (0.5, 0.5, 0) with the appearance of superstructure peaks could be clearly identified. The large tail of the superstructure intensity above the CDW transition indicates the importance of critical fluctuations.
SiMufti, N.*; 金子 耕士; Hoser, A.*; Gutmann, M.*; Geibel, C.*; Krellner, C.*; Stockert, O.*
Physical Review B, 94(4), p.045116_1 - 045116_8, 2016/07
被引用回数：2 パーセンタイル：10.64(Materials Science, Multidisciplinary)We report on the results of powder and single crystal neutron diffraction to investigate the magnetic order in YbCoSi below the N
el temperature 
,K in detail. Two different magnetically ordered phases can clearly be distinguished. At lowest temperatures a commensurate magnetic structure with a propagation vector 
is found, while the intermediate phase (
,K) is characterized by an incommensurate magnetic structure with 
. The magnetic structure in YbCoSi is in marked contrast to all other known 
CoSi compounds ( = rare earth element) likely due to some itineracy of the Yb 4f states being responsible for the magnetism.
Si金子 耕士; Stockert, O.*; F
k, B.*; Raymond, S.*; Skoulatos, M.*; 竹内 徹也*; 大貫 惇睦*
Physical Review B, 89(24), p.241105_1 - 241105_5, 2014/06
被引用回数：2 パーセンタイル：9.77(Materials Science, Multidisciplinary)The effect of magnetic field on the static and dynamic spin correlations in the non-centrosymmetric heavy-fermion superconductor CePtSi was investigated by neutron scattering. The application of a magnetic field B increases the antiferromagnetic (AFM) peak intensity. This increase depends strongly on the field direction: for 
the intensity increases by a factor of 4.6 at a field of 6.6T, which corresponds to more than a doubling of the AFM moment, while the moment increases by only 10% for 
at 5T. This is in strong contrast to the inelastic response near the antiferromagnetic ordering vector, where no marked field variations are observed for up to 3.8T. The results reveal that the AFM state in CePtSi, which coexists with superconductivity, is distinctly different from other unconventional superconductors.
Si金子 耕士; Stockert, O.*; Skoulatos, M.*; Schneidewind, A.*; 竹内 徹也*; 松田 達磨; 芳賀 芳範; 摂待 力生*; 大貫 惇睦; 目時 直人
Journal of the Physical Society of Japan, 81(Suppl.B), p.SB006_1 - SB006_7, 2012/12
被引用回数：3 パーセンタイル：26.68(Physics, Multidisciplinary)The discovery of heavy-fermion superconductivity in non-centrosymmetric compound CePtSi, and subsequent findings of Ce
(T: transition metal, X: Si, Ge) bring a new essence in the condensed matter physics, since a novel type of superconducting properties is expected to come out. In CePtSi, the compound shows an antiferromagnetic (AFM) order at 
=2.2 K and enters into a heavy-fermion superconducting state below 
0.5 K. Through neutron scattering experiments under external magnetic field, we identified anomalous field response in CePtSi in the AFM state; AFM intensity showed enormous enhancement with increasing an applied field. The intensity kept increasing up to 7 T with the kink at around the additional phase boundary. These features suggest that the magnetic order in CePtSi is not a simple AFM one, and imply that large fraction of magnetic response could be still missing in this compound.
Si金子 耕士; Stockert, O.*; Mufti, N.*; Kiefer, K.*; Klingner, C.*; Krellner, C.*; Geibel, C.*; Steglich, F.*
Journal of Physics; Conference Series, 200, p.032031_1 - 032031_4, 2010/02
被引用回数：5 パーセンタイル：84.49(Materials Science, Multidisciplinary)YbCoSi with the tetragonal ThCrSi-type structure is an isoelectronic compound to YbRhSi. At zero magnetic field YbCoSi undergoes two magnetic transitions at 
=0.9,K and 
=1.7,K,and exhibits a complex magnetic phase diagram for small applied fields, lower than 
=2,T. Therefore, YbCoSi is not only a good reference to YbRhSi but also an interesting system in its own to study its magnetic properties. In order to reveal the magnetic structure of YbCoSi, a neutron powder diffraction experiment was carried out. At zero field, several superlattice reflections were clearly observed at 0.5,K. By heating up to 1.1,K, to the intermediate phase, a substantial change in both, the peak position and the intensity ratio of the magnetic reflection was found. We will propose a possible magnetic structure for both phases.
Si金子 耕士; Stockert, O.*; Arndt, J.*; Borth, R.*; Skoulatos, M.*; Habicht, K.*; Kiefer, K.*; Schneidewind, A.*; Etzdorf, D.*; 竹内 徹也*; et al.
no journal, ,
The heavy-fermion superconductivity in CePtSi with a non-centrosymmetric structure attracts a lot of attention since novel superconducting properties are expected under this symmetry. Another characteristics of the superconductivity in CePtSi is its coexistence with long-range antiferromagnetic order. Therefore detailed antiferromagnetic properties and its interplay with superconductivity are of strong interest to investigate. The magnetic structure of CePtSi is represented by 
=(0,0,1/2). We have observed that the 0 0 1/2 antiferromagnetic reflection exhibits a peculiar response to an external magnetic field; its intensity increases with magnetic fields. These results imply unusual antiferromagnetism in CePtSi.
Si金子 耕士; Stockert, O.*; Arndt, J.*; Borth, R.*; Skoulatos, M.*; Habicht, K.*; Kiefer, K.*; Schneidewind, A.*; Etzdorf, D.*; 竹内 徹也*; et al.
no journal, ,
The heavy-fermion superconductivity in CePtSi with a non-centrosymmetric structure attracts a lot of attention since novel superconducting properties are expected under this symmetry. Another characteristics of the superconductivity in CePtSi is its coexistence with long-range antiferromagnetic order. Therefore detailed antiferromagnetic properties and its interplay with superconductivity are of strong interest to investigate. The magnetic structure of CePtSi is represented by 
=(0,0,1/2). We have observed that the 0 0 1/2 antiferromagnetic reflection exhibits a peculiar response to an external magnetic field; its intensity increases with magnetic fields. These results imply unusual antiferromagnetism in CePtSi.
Siにおける磁気転移金子 耕士; Stockert, O.*; Mufti, N.*; Kiefer, K.*; Klingner, C.*; Krellner, C.*; Geibel, C.*; Steglich, F.*
no journal, ,
YbCoSiは、
=0.9K, 
=1.7Kの2段の磁気転移を示すことが明らかとなった。また2T以下の低磁場で多段の磁気転移を示す、複雑な磁気相図が報告された。YbCoSiの磁気構造の決定とともに、この系の磁気相互作用を明らかにする目的で、中性子回折実験を行った。実験は、ベルリンのBER-II原子炉に設置されたE2において行った。粉末中性子回折パターンから、常磁性状態(2.0K)の結果を差し引いたものにおいて、明瞭な磁気反射の観測に成功した。0.48Kで観測された磁気反射は、1.1Kへの昇温に伴い、低角側にシフトするとともに、その強度比が大きく変化することを見いだした。今回観測された磁気反射は、磁気秩序を示す他のCoSi(=希土類)において観測される100, 001とは異なっており、YbCoSiの磁気秩序相は、単純な整合反強磁性構造ではないことを示している。当日は単結晶の結果と合わせて、その磁気構造について報告する。
Si金子 耕士; Stockert, O.*; Skoulatos, M.*; Schneidewind, A.*; 竹内 徹也*; 松田 達磨; 芳賀 芳範; 摂待 力生*; 大貫 惇睦; 目時 直人
no journal, ,
CePtSi without inversion symmetry exhibits an antiferromagnetic (AFM) order at 2.2 K and enters into a heavy-fermion superconducting state below 0.5 K. Additional anomalies inside the AFM state were found under external magnetic fields in the vicinity of the upper critical field of the superconducting state. Our neutron scattering experiments under magnetic fields revealed that the application of the magnetic fields leads to an enormous enhancement in the AFM peak intensity in CePtSi, opposite to what is observed in usual antiferromagnets. We have clarified that the reported anomaly under the magnetic fields corresponds to inflection points in the field variation of the AFM intensity. The observed huge increase in AFM intensity corresponds to an increase of the ordered moment under the magnetic fields. These results imply an existence of a missing magnetic response in the ground state, which might be related to the formation of the superconducting state in CePtSi.
Si金子 耕士; Stockert, O.*; Skoulatos, M.*; Schneidewind, A.*; 竹内 徹也*; 松田 達磨; 芳賀 芳範; 摂待 力生*; 大貫 惇睦; 目時 直人
no journal, ,
The discovery of heavy-fermion superconductivity in non-centrosymmetric compound CePtSi brings a new essence in the field of condensed matter physics, since a novel type of superconducting properties are expected to emerge. CePtSi shows an antiferromagnetic (AFM) order at 
=2.2 K and enters into a heavy-fermion superconducting state below 
0.5 K. We identified anomalous external magnetic field response in CePtSi by neutron scattering experiments in the AFM state. An observed huge increase in AFM intensity corresponds to an increase of the staggered moment under uniform field, opposite of what is observed in ordinary antiferromagnets. These features suggest that the magnetic order in CePtSi is not a simple AFM one, and imply that large fraction of magnetic response could be still missing in this compound.
Al and UPdAlScheneidewind, A.*; Hiess, A.*; Stockert, O.*; 阿曽 尚文*; 佐藤 憲昭*; Raymond, S.*; 金子 耕士; Blackburn, E.*; Steffens, P.*; Lander, G. H.*
no journal, ,
Inelastic neutron scattering (INS) has been of particular importance in studying the interrelation of magnetism and superconductivity by determining the momentum- and energy-dependent microscopic spin dynamics in both the normal and superconducting state. In this context, we recently revisited the spin dynamics in the iso-structural magnetic superconductors UPdAl (
= 2K) and UNiAl ( = 1K). The magnetic order in UPdAl is commensurate with 
= (0, 0, 0.5), but incommensurate in UNiAl with 
= (0.39, 0, 0.5). We here present new INS results on the normal state spin dynamics of UNiAl in high resolution TAS mode as well as with the FlatCone set-up, and the influence of magnetic field on the spin dynamics in the superconducting state in UPdAl with a half-polarized setup.
Si金子 耕士; Stockert, O.*; 田端 千紘; 桑原 慶太郎*; 鬼柳 亮嗣; 中尾 朗子*; Krellner, C.*; Geibel, C.*
no journal, ,
Novel physical phenomena, such as superconductivity and non-Fermi liquid behavior, emerge in the vicinity of a quantum critical point (QCP). YbRhSi has been extensively studied owing to its proximity to an antiferromagnetic (AFM) QCP at ambient pressure. The AFM order at = 70 mK is suppressed by a weak external magnetic field. An inelastic neutron scattering study revealed a competition between ferromagnetic and incommensurate spin fluctuations at q' close to the zone center in YbRhSi, and evolution of resonance-like response at q=0 under magnetic fields. These features suggest an importance of ferromagnetic fluctuations in this system, where as a static AFM order was not confirmed at q'. This fact indicates that the AFM order in YbRhSi may have a different characteristic wave vector. As the latest study discovers emergence of superconductivity at very low temperature, recurring interests on nature of the AFM order burst. A search for an AFM Bragg reflection in YbRhSi has extreme difficulties arising from extremely low , and correspondingly a tiny ordered moment. To overcome these difficulties, we focus on isoelectronic substitution, where substitution of Rh with Co leads to a stabilization of the magnetic order. The huge enhancement of through the Co doping provides us with an opportunity to study the magnetic order closely. Our latest single crystal neutron scattering experiment was carried out on a lower Co concentration of 0.18. A new form of the AFM ordering vector was revealed in the ground state. This provides new insights into magnetic properties of YbRhSi.
