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Journal Articles

Field-angular dependence of pairing interaction in URhGe; Comparison with UCoGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; et al.

JPS Conference Proceedings (Internet), 30, p.011037_1 - 011037_6, 2020/03

The field-angular dependence of Co-NMR spin-lattice relaxation rate $$1/T_1$$ has been measured for a 10% Co-doped single crystal of URhGe. The experiment revealed that spin fluctuations in ferromagnetic (FM) state of URhGe are robust against magnetic field below about 4 T, applied along any direction in the $$bc$$ crystal plane. This is in clear contrast with the sister compound UCoGe, in which FM spin fluctuations are rapidly suppressed by a tiny applied field along the $$c$$ axis. We show that such a difference in the character of the spin fluctuations is reflected in their two distinct phase diagrams for the upper critical field $$H_{rm c2}$$, providing further support to the mechanism of superconductivity mediated by spin fluctuations in these materials.

Journal Articles

High-field phase diagram of the heavy-fermion metal CeIn$$_3$$; Pulsed-field NMR study on single crystals up to 56 T

Tokunaga, Yo; Orlova, A.*; Bruyant, N.*; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Higa, Nonoka; et al.

Physical Review B, 99(8), p.085142_1 - 085142_5, 2019/02

 Times Cited Count:5 Percentile:28.12(Materials Science, Multidisciplinary)

The heavy-fermion antiferromagnet CeIn$$_3$$ exhibits a field-induced anomaly associated with Fermi surface reconstruction at $$H^*sim$$ 45 T, well below the antiferromagnetic (AFM) critical field that exceeds 60 T. In order to explore the origin of this anomaly, we have measured $$^{115}$$In NMR spectra in pulsed magnetic fields up to 56 T using high-quality single crystals. To within experimental resolution, we do not detect any change in the NMR spectra that could suggest a modification in either the character of the hyperfine field or the electric field gradient at In sites through $$H^*$$. This strongly suggests that the 45 T anomaly cannot be simply ascribed to a field-induced change in the magnetic structure of the AFM state.

Journal Articles

Interplay between quantum fluctuations and reentrant superconductivity with a highly enhanced upper critical field in URhGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku; et al.

Physical Review B, 93(20), p.201112_1 - 201112_5, 2016/05

 Times Cited Count:13 Percentile:52.76(Materials Science, Multidisciplinary)

The ferromagnetic superconductor URhGe has been known to exhibit an extremely large enhancement of the upper critical field when the field is confined and rotated in the ($$ab$$) crystal plane. Our high-field $$^{59}$$Co NMR measurements on 10% Co-doped URhGe up to 30 T prove that this unconventional behavior of the superconductivity (SC) is associated with a strong anisotropy of field-dependent quantum fluctuations near a tricritical point. These fluctuations are rapidly suppressed by the field component along the $$c$$ axis, while being unaffected by any field component along the $$a$$ axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.

Journal Articles

Quantum tricritical fluctuations driving mass enhancement and reentrant superconductivity in URhGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; et al.

Journal of Physics; Conference Series, 683(1), p.012010_1 - 012010_6, 2016/02

 Times Cited Count:0 Percentile:0.03

Metamagnetism is in itself quite interesting phenomena, especially in a system with itinerant f-electrons. Unconventional states observed in the vicinity of the metamagnetic transition have been the subject of a number of recent publications. The object of this study is to elucidate the interplay between superconductivity and metamagnetism in URhGe. The nature of the metamagnetism becomes particularly important in ferromagnetic superconductors URhGe and UCoGe, since it is likely related to the pairing mechanism for their unconventional superconductivity. Here we report the result of our Co-NMR study on URh$$_{1-x}$$Co$$_{x}$$Ge and discuss the origin of the field induced superconducting phenomenon observed in high fields around 12 T.

Journal Articles

Reentrant superconductivity driven by quantum tricritical fluctuations in URhGe; Evidence from $$^{59}$$Co NMR in URh$$_{0.9}$$Co$$_{0.1}$$Ge

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Kambe, Shinsaku; Araki, Shingo*

Physical Review Letters, 114(21), p.216401_1 - 216401_5, 2015/05

 Times Cited Count:49 Percentile:89.36(Physics, Multidisciplinary)

Our measurements of the $$^{59}$$Co NMR spin-spin relaxation in URh$$_{0.9}$$Co$$_{0.1}$$Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at $$H_Rapprox13$$ T, around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We show that critical fluctuations develop in the same limited region near the field $$H_R$$ as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point.

Oral presentation

NMR study on U(Rh$$_{1-x}$$Co$$_{x}$$)Ge

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Kambe, Shinsaku

no journal, , 

The object of this study is to elucidate the interplay between superconductivity and metamagnetism in URhGe. Metamagnetism is in itself quite interesting phenomena, especially in a system with itinerant f-electrons. Unconventional states observed in the vicinity of the metamagnetic transition have been the subject of a number of recent publications. The nature of the metamagnetism becomes particularly important in ferromagnetic superconductors URhGe and UCoGe, since it is likely related to the pairing mechanism for their unconventional superconductivity. Here we report the result of our NMR study on U(Rh$$_{1-x}$$Co$$_{x}$$)Ge.

Oral presentation

NMR study on U(Rh$$_{1-x}$$Co$$_{x}$$)Ge, 2

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Kambe, Shinsaku

no journal, , 

no abstracts in English

Oral presentation

NMR study on U(Rh$$_{1-x}$$Co$$_{x}$$)Ge, 3

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Hattori, Taisuke; Sakai, Hironori; Kambe, Shinsaku; et al.

no journal, , 

no abstracts in English

Oral presentation

NMR study on URhGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Hattori, Taisuke; Sakai, Hironori; Kambe, Shinsaku; et al.

no journal, , 

no abstracts in English

Oral presentation

NMR study on a single crystal of URhGe

Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku; et al.

no journal, , 

Ferromagnetism is incompatible in general with superconductivity (SC) with singlet spin pairs, since a strong exchange field in ferromagnetic state forces the spin pairs to align in the same direction. In contrast, fluctuation of ferromagnetic moments has been supposed to create a binding force between quasi-particles with triplet spin. Such an unconventional spin-triplet state, mediated by ferromagnetic fluctuations, is now expected to be realized in a family of uranium based compounds, UGe$$_2$$, URhGe and UCoGe, so far the only fully established examples of ferromagnetic superconductors in which uniform SC is realized deep inside the ferromagnetic states. To elucidate the mechanism of this exotic SC, we have prepared a URhGe single crystal and performed nuclear magnetic resonance (NMR) experiments.

Oral presentation

Pulsed high-field NMR study on CeIn$$_3$$; High-field phase diagram near an antiferromagnetic QCP

Tokunaga, Yo; Orlova, A.*; Bruyant, N.*; Aoki, Dai*; Mayaffre, H.*; Kr$"a$mer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati$'c$, M.*; Sakai, Hironori; et al.

no journal, , 

In order to understand the origin of the field-induced anomaly observed in the heavy-fermion metal CeIn$$_3$$ at about 45 T, well before the antiferromagnetic critical field, we have performed a pulsed magnetic field In-NMR study using a single crystal up to 56 Tesla. We confirmed that there is no obvious change of hyperfine fields at In sites even above 45 T. This indicates that there is no structural change at high fields, and further, denies simple explanations of the anomaly as due to a field-induced change of the magnetic structure in CeIn$$_3$$.

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