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論文

Feedback of superconductivity on the magnetic excitation spectrum of UTe$$_{2}$$

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

Journal of the Physical Society of Japan, 90(11), p.113706_1 - 113706_5, 2021/11

We investigate the spin dynamics in the superconducting phase of UTe$$_2$$ by triple-axis inelastic neutron scattering on a single crystal sample. At the wave-vector $$k_1$$ = (0, 0.57, 0), where the normal state antiferromagnetic correlations are peaked, a modification of the excitation spectrum is evidenced, on crossing the superconducting transition, with a reduction of the relaxation rate together with the development of an inelastic peak at $${Omega} approx$$ 1 meV. The low dimensional nature and the a-axis polarization of the fluctuations, that characterise the normal state, are essentially maintained below Tsc. The high ratio of $${Omega}$$ $$k_{rm B}$$$$T$$$$_{sc}$$ $$approx$$ 7.2 contrasts with the most common behaviour in heavy fermion superconductors.

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

Fermi surface in the hidden-order state of URu$$_2$$Si$$_2$$ under intense pulsed magnetic fields up to 81T

Scheerer, G. W.*; Knafo, W.*; 青木 大*; Nardone, M.*; Zitouni, A.*; B$'e$ard, J.*; Billette, J.*; Barata, J.*; Jaudet, C.*; Suleiman, M.*; et al.

Physical Review B, 89(16), p.165107_1 - 165107_12, 2014/04

 被引用回数:10 パーセンタイル:47.27(Materials Science, Multidisciplinary)

Fermi surface of URu$$_2$$Si$$_2$$ has been studied by measuring the quantum oscillation at low temperature and high magnetic field up to 81T. The data suggest interplay between Fermi surface, magnetic properties and the hidden order.

論文

Field-induced phenomena in ferromagnetic superconductors UCoGe and URhGe

青木 大*; Taupin, M.*; Paulsen, C.*; Hardy, F.*; Taufour, V.*; 小手川 恒*; Hassinger, E.*; Malone, L.*; 松田 達磨; 三宅 厚志*; et al.

Journal of the Physical Society of Japan, 81(Suppl.B), p.SB002_1 - SB002_6, 2012/12

 被引用回数:3 パーセンタイル:28.92(Physics, Multidisciplinary)

We review our recent studies on ferromagnetic superconductors, UGe2, URhGe, and UCoGe. We focus on experimental results of URhGe and UCoGe in which the superconductivity occurs already at ambient pressure. The huge upper critical field $$H$$$$_{c2}$$ on UCoGe for the field along the hard magnetization axis ($$b$$-axis) is confirmed by the AC susceptibility measurements by the fine tuning of field angle. Contrary to the huge $$H$$$$_{c2}$$ along the hard-magnetization axis, $$H$$$$_{c2}$$ along the easy-magnetization axis ($$c$$-axis) is relatively small in value. However, the initial slope of $$H$$$$_{c2}$$, namely $$d$$$$H$$$$_{c2}$$/$$dT$$ ($$H$$$$rightarrow$$0) both in UCoGe and in URhGe indicates the large value, which can be explained by the magnetic domain effect detected in the magnetization measurements. The specific heat measurements using a high quality single crystal of UCoGe demonstrate the bulk superconductivity, which is extended under magnetic field for the field along $$c$$-axis.

論文

High-field moment polarization in the ferromagnetic superconductor UCoGe

Knafo, W.*; 松田 達磨; 青木 大*; Hardy, F.*; Scheerer, G. W.*; Ballon, G.*; Nardone, M.*; Zitouni, A.*; Meingast, C.*; Flouquet, J.*

Physical Review B, 86(18), p.184416_1 - 184416_4, 2012/00

 被引用回数:38 パーセンタイル:83.43(Materials Science, Multidisciplinary)

We report magnetization and magnetoresistivity measurements on the isostructural ferromagnetic superconductors UCoGe and URhGe in magnetic fields up to 60 T and temperatures from 1.5 to 80 K. At low temperature, a moment polarization in UCoGe in a field $$mu_0$$H $$||$$ b of around 50T leads to well-defined anomalies in both magnetization and magnetoresistivity. These anomalies vanish in temperatures higher than 30-40 K, where maxima in the magnetic susceptibility and the field-induced variation of the magnetoresistivity are found. A comparison is made between UCoGe and URhGe, where a moment reorientation in a magnetic field $$mu_0$$H $$||$$ b of 12T leads to field-induced reentrant superconductivity.

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