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論文

Low-dimensional antiferromagnetic fluctuations in the heavy-fermion paramagnetic ladder compound UTe$$_{2}$$

Knafo, W.*; Knebel, G.*; Steffens, P.*; 金子 耕士; Rosuel, A.*; Brison, J.-P.*; Flouquet, J.*; 青木 大*; Lapertot, G.*; Raymond, S.*

Physical Review B, 104(10), p.L100409_1 - L100409_6, 2021/09

 被引用回数:0 パーセンタイル:0(Materials Science, Multidisciplinary)

Inelastic-neutron-scattering measurements were performed on a single crystal of the heavy-fermion paramagnet UTe$$_{2}$$ above its superconducting temperature. We confirm the presence of antiferromagnetic fluctuations with the incommensurate wave-vector $${bf K}_{1}$$ = (0, 0.57, 0). A quasielastic signal is found, whose momentum-transfer dependence is compatible with fluctuations of magnetic moments $$mu$$ $$||$$ ${bf a}$, with a sine-wave modulation of wave-vector $${bf K}_{1}$$ and in-phase moments on the nearest U atoms. Low dimensionality of the magnetic fluctuations, consequence of the ladder structure, is indicated by weak correlations along the direction ${bf c}$. These results constitute constraints for models of magnetically-mediated superconductivity in UTe$$_{2}$$.

論文

Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe$$_{2}$$Ge$$_{2}$$

Wo, H.*; Wang, Q.*; Shen, Y.*; Zhang, X.*; Hao, Y.*; Feng, Y.*; Shen, S.*; He, Z.*; Pan, B.*; Wang, W.*; et al.

Physical Review Letters, 122(21), p.217003_1 - 217003_5, 2019/05

 被引用回数:2 パーセンタイル:35.62(Physics, Multidisciplinary)

We report neutron scattering measurements of single-crystalline YFe$$_{2}$$Ge$$_{2}$$ in the normal state, which has the same crystal structure as the 122 family of iron pnictide superconductors. YFe$$_{2}$$Ge$$_{2}$$ does not exhibit long-range magnetic order but exhibits strong spin fluctuations. Like the iron pnictides, YFe$$_{2}$$Ge$$_{2}$$ displays anisotropic stripe-type antiferromagnetic spin fluctuations at ($$pi, 0, pi$$). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wave vector ($$0, 0, pi$$). These ferromagnetic spin fluctuations are isotropic in the ($$H, K$$) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe$$_{2}$$Ge$$_{2}$$ and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.

論文

Evidence for three fluctuation channels in the spin resonance of the unconventional superconductor CeCoIn$$_5$$

Raymond, S.*; 金子 耕士; Hiess, A.*; Steffens, P.*; Lapertot, G.*

Physical Review Letters, 109(23), p.237210_1 - 237210_5, 2012/12

 被引用回数:17 パーセンタイル:70.21(Physics, Multidisciplinary)

Polarized inelastic neutron scattering under magnetic field is used to get a microscopic insight into the spin resonance of the heavy fermion superconductor CeCoIn$$_5$$. The resonance lineshape is found to depend on the neutron polarization: Some of the spectral weight is common to the two polarization channels while the remaining part is distributed equally between them. This is evidence for the spin resonance being a degenerate mode with three fluctuation channels: A Zeeman split contribution and an additional longitudinal mode.

口頭

Effect of magnetic field on magnetic excitation in heavy-fermion superconductors probed via neutron scattering

金子 耕士; Raymond, S.*; Hiess, A.*; F${aa}$k, B.*; Steffens, P.*; Lapertot, G.*; 摂待 力生*; 大貫 惇睦

no journal, , 

An interplay between magnetism and superconductivity is one of the main research subjects in the field of strongly correlated electron systems. Magnetic excitation of heavy-fermion superconductor CeCoIn$$_{5}$$ (CCI5), which has the highest $$T_{rm sc}$$ of 2.3 K among the Ce-based heavy-fermion superconductors, exhibits distinct change; a quasielastic magnetic response above $$T_{rm sc}$$ turns into spin resonance below $$T_{rm sc}$$. Contrasting behaviour was obtained in non-centrosymmetric heavy-fermion superconductor CePt$$_3$$Si (CP3S) with $$T_{rm N}$$ = 2.2 K and $$T_{rm sc}{sim}$$ 0.5 K. In CP3S, identical magnetic excitation spectra have been observed below and above $$T_{rm sc}$$. Instead, an external magnetic field induces a drastic enhancement of the antiferromagnetic moment. We will show our latest results on neutron scattering study under magnetic field to get insights into the nature of resonance in CCI5, and the origin of the antiferromagnetic moment enhancement in CP3S.

口頭

重い電子系超伝導体CeCoIn$$_5$$におけるカイラリティを持つスピンレゾナンス

Raymond, S.*; 金子 耕士; Hiess, A.*; Steffens, P.*; Lapertot, G.*

no journal, , 

"スピンレゾナンス"は、銅酸化物や、鉄系、そして重い電子系などの非従来型超伝導体に共通して観測される磁気励起で、超伝導ギャップ$$delta$$が符号を変える波数において、$${Omega}_{res}$$/2$${Delta}{sim}$$0.64となるエネルギーに観測される。その起源についての共通した理解はまだ得られていない一方、レゾナンスピークは、超伝導の対称性や性質についての知見をもたらすことから、重要な応答である。重い電子系超伝導体では、UPd$$_2$$Al$$_3$$, CeCu$$_2$$Si$$_2$$, CeCoIn$$_5$$において、スピンレゾナンスが観測されている。今回、Ce系重い電子系超伝導体で最も高い$$T_{sc}$$=2.3Kを示すCeCoIn$$_5$$を対象として、磁場下での偏極非弾性散乱実験を行い、その詳細を調べた。その結果、CeCoIn$$_5$$におけるスピンレゾナンスは縮退したモードであり、磁場によりゼーマン分裂を示すことを明らかにした。さらに片側偏極の解析結果から、分裂したピークは、各々のカイラリティを持つ2成分に加え、カイラリティを持たない1成分、合わせて3成分からなることを見いだした。これらの事実は、今後の理論研究を進めるうえで、重要な制約として機能することが期待される。

口頭

重い電子系超伝導体CeCoIn$$_5$$におけるカイラリティを持つスピンレゾナンス

Raymond, S.*; 金子 耕士; Hiess, A.*; Steffens, P.*; Lapertot, G.*

no journal, , 

銅酸化物や重い電子系など、非従来型超伝導体に共通して観測されるスピンレゾナンスは、その起源について統一した理解は得られていない一方、超伝導の対称性や性質についての知見をもたらすことから、重要な応答である。重い電子系超伝導体のうち、今回、Ce系重い電子系超伝導体でもっとも高い$$T_{rm sc}$$を示すCeCoIn$$_5$$を対象として、磁場下での偏極非弾性散乱実験を行い、その詳細を調べた。その結果、入射偏極状態に依存して、スペクトルが大きく変化していることを見いだした。片側偏極の解析結果から、レゾナンスピークが磁場によりゼーマン分裂を示すこと、さらに分裂したピークは、各々のカイラリティを持つ2成分に加え、カイラリティを持たない1成分、合わせて3成分からなることを見いだした。これらの事実は、CeCoIn$$_5$$における強い常磁性効果の存在とともに、スピンレゾナンスが縮退したモードであることを示している。

口頭

Presence of chiral character in the spin resonance of the unconventional superconductor CeCoIn$$_5$$

Raymond, S.*; 金子 耕士; Hiess, A.*; Steffens, P.*; Lapertot, G.*

no journal, , 

In various unconventional superconductors, there exists characteristic magnetic response so-called "spin resonance". This mode is observed in inelastic neutron scattering below the superconducting transition temperature Tc at the wave vector for which the superconducting gap changes sign and at an energy $${Omega}_{rm res}/2{Delta}{sim}$$ 0.64. In order to get microscopic insights into the spin resonance, the heavy-fermion superconductor CeCoIn$$_5$$ was investigated via polarized inelastic neutron scattering under a magnetic field. We found that the spin resonance at 0.6 meV at zero field splits under magnetic fields. The magnetic excitation under the field is characterized as two Zeeman split peaks with a chiral nature, and an additional non-chiral contribution that appears at the same energy as the lower mode of the Zeeman split peaks. This observation evidences that the spin resonance in CeCoIn$$_5$$ is a degenerated mode, which has three fluctuation channels under magnetic field.

口頭

New neutron scattering results on the spin dynamics in UNi$$_2$$Al$$_3$$ and UPd$$_2$$Al$$_3$$

Scheneidewind, 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 UPd$$_2$$Al$$_3$$ ($$T_c$$ = 2K) and UNi$$_2$$Al$$_3$$ ($$T_c$$ = 1K). The magnetic order in UPd$$_2$$Al$$_3$$ is commensurate with $$Q_0$$ = (0, 0, 0.5), but incommensurate in UNi$$_2$$Al$$_3$$ with $$Q^*$$ = (0.39, 0, 0.5). We here present new INS results on the normal state spin dynamics of UNi$$_2$$Al$$_3$$ 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 UPd$$_2$$Al$$_3$$ with a half-polarized setup.

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