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Journal Articles

Nanoscale heterogeneity induced by nonmagnetic Zn dopants in the quantum critical metal CeCoIn$$_5$$; $$^{115}$$In NQR/NMR and $$^{59}$$Co NMR study

Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Zhu, J.-X.*; Ronning, F.*; Thompson, J. D.*; Ramakrishna, S. K.*; Reyes, A. P.*; Suzuki, Kohei*; Oshima, Yoshiki*; et al.

Physical Review B, 104(8), p.085106_1 - 085106_12, 2021/08

Antiferromagnetism in a prototypical quantum critical metal CeCoIn$$_5$$ is known to be induced by slight substitutions of non-magnetic Zn atoms for In. In nominally 7% Zn substituted CeCoIn$$_5$$, an antiferromagnetic (AFM) state coexists with heavy fermion superconductivity. Heterogeneity of the electronic states is investigated in Zn doped CeCoIn$$_5$$ by means of nuclear quadrupole and magnetic resonances (NQR and NMR). Site-dependent NQR relaxation rates $$1/T_1$$ indicate that the AFM state is locally nucleated around Zn substituents in the matrix of a heavy fermion state, and percolates through the bulk at the AFM transition temperature $$T_{rm N}$$. At lower temperatures, an anisotropic superconducting (SC) gap below the SC transition temperature $$T_{rm c}$$, and the SC state permeates through the AFM regions via a SC proximity effect. Applying an external magnetic field induces a spin-flop transition near 5 T, reducing the volume of the AFM regions. Consequently, a short ranged inhomogeneous AFM state survives and coexists with a paramagnetic Fermi liquid state at high fields.

Journal Articles

NMR shift measurements of $$^{69}$$Ga in unconventional superconductor PuRhGa$$_{5}$$

Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 75(Suppl.), p.50 - 52, 2006/08

Very recently, we have succeeded in NMR/NQR measurements for PuRhGa$$_{5}$$. PuRhGa$$_{5}$$ is a superconductor with $$T_{c}$$$$approx$$9 K, which is isomorphic to PuCoGa$$_{5}$$ with the higher $$T_{c}$$=18 K. We have reported that PuRhGa$$_{5}$$ is an unconventional superconductor with an anisotropic gap, through the measurement of NQR spin-lattice relaxation rate $$1/T_{1}$$ , while PuCoGa$$_{5}$$ is also reported to be such an anisotropic superconductor. The Knight shift $$K$$ and $$1/T_{1}$$ of NMR under applied field for the normal state of PuRhGa$$_{5}$$ suggest an anisotropic feature of hyperfine and/or spin fluctuation in this system. We will outline the superconducting state and report the nature of the normal state based on the basis of $$K$$ and $$1/T_{1} T$$ results. The difference between PuRhGa$$_{5}$$ and PuCoGa$$_{5}$$ will be also discussed.

Journal Articles

Unconventional superconductivity in PuRhGa$$_{5}$$; Ga NMR/NQR study

Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Physica B; Condensed Matter, 378-380, p.1005 - 1006, 2006/05

 Times Cited Count:6 Percentile:32.73(Physics, Condensed Matter)

$$^{69,71}$$ Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa$$_{5}$$ with $$T_{c}$$=9 K. The spin-lattice relaxation rate $$1/T_{1}$$ reveals that PuRhGa$$_{5}$$ is an unconventional superconductor having an anisotropic superconducting gap. Moreover, Korringa behavior ($$1/T_{1} T = const.$$) is observed in the normal state below 30 K. This result suggests that the superconductivity sets in after the formation of a Fermi liquid state in this compound.

Journal Articles

Anisotropic superconducting gap in transuranium superconductor PuRhGa$$_{5}$$; Ga NQR study on a single crystal

Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.

Journal of the Physical Society of Japan, 74(6), p.1710 - 1713, 2005/06

 Times Cited Count:78 Percentile:90.85(Physics, Multidisciplinary)

$$^{69,71}$$Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa$$_{5}$$ with $$T_{c}sim 9$$ K. We have observed a $$^{69}$$Ga NQR line at $$sim$$29.15 MHz, and assigned it to the $$4i$$ Ga site using the NMR results. The $$^{69}$$Ga NQR spin-lattice relaxation rate $$1/T_{1}$$ shows no coherence peak just below $$T_{rm c}$$, but obeys $$T^{3}$$ behavior below $$T_{rm c}$$. This result strongly suggests that PuRhGa$$_{5}$$ is an unconventional superconductor having an anisotropic superconducting gap. The gap amplitude 2$$Delta_{0}(Trightarrow 0)simeq5k_{rm B}T_{rm c}$$ and the residual density of states $$N_{rm res}(T=0)/N_{rm 0}(T=T_{rm c})simeq$$ 0.25 have been determined assuming a simple polar function of the form $$Delta(theta,phi)$$=$$Delta_{0}costheta$$, where $$theta$$ and $$phi$$ are angular parameters on the Fermi surface.

Journal Articles

NQR measurements of UTGa$$_{5}$$

Kato, Harukazu; Sakai, Hironori; Kambe, Shinsaku; Walstedt, R. E.; Tokiwa, Yoshifumi; Onuki, Yoshichika

Acta Physica Polonica B, 34(2), p.1063 - 1066, 2003/09

We performed $$^{69,71}$$Ga-NMR/NQR studies for UPtGa$$_{5}$$, which is a 5$$f$$-itinerant antiferromagnets with Neel temperature $$T_{N}$$ = 26 K and an electronic specific coefficient $$gamma$$ = 57 mJ/mol K$$^{2}$$. From the NMR spectrum in the paramagnetic temperature region, the hyperfine coupling constants $$A_{hf}^{para}$$ in the paramagnetic state have been evaluated. The magnitude of the transferred field has been evaluated from the zero-applied-field spectrum, yielding a value for the hyperfine coupling constant $$A_{hf}^{AF}$$ in the antiferromagnetic state. The estimated value of $$A_{hf}^{AF}$$ is an order of magnitude larger than that of $$A_{hf}^{para}$$. This implies the existence of a long-ranged hyperfine interaction path. The mechanism of the hyperfine interaction will be discussed in terms of RKKY interactions.

Journal Articles

Ga and Pt NMR study of UPtGa$$_{5}$$

Kato, Harukazu; Sakai, Hironori; Tokiwa, Yoshifumi; Kambe, Shinsaku; Walstedt, R. E.; Onuki, Yoshichika

Journal of Physics and Chemistry of Solids, 63(6-8), p.1197 - 1200, 2002/06

 Times Cited Count:10 Percentile:49.22(Chemistry, Multidisciplinary)

no abstracts in English

Journal Articles

Ga NMR/NQR study in UGa$$_{3}$$

Ikushima, Kenji; Aoki, Dai*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika

Journal of Magnetism and Magnetic Materials, 226-230(Part.1), p.89 - 91, 2001/05

no abstracts in English

Journal Articles

Unusual phase transition of UGa$$_{3}$$ observed by Ga NQR

Ikushima, Kenji; Aoki, Dai*; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika; Kambe, Shinsaku; Walstedt, R. E.

Journal of the Physical Society of Japan, Vol.70, Supplement A, p.31 - 33, 2001/05

no abstracts in English

Journal Articles

Spin and charge in exotic oxides explored by NMR/NQR observations

Yasuoka, Hiroshi

Journal of the Physical Society of Japan, 69(suppl.B), p.161 - 172, 2000/00

no abstracts in English

Journal Articles

Scaling behavior in the Ce-based Kondo semiconductors; NQR/NMR measurements of CeRhSb and CeNiSn under high pressures

Ikushima, Kenji; Yasuoka, Hiroshi; Uwatoko, Yoshiya*; Ishikawa, Yoshikazu*

Physical Review B, 60(21), p.14537 - 14540, 1999/00

 Times Cited Count:5 Percentile:34.48(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

How to generate a Kondo hole; A Heavy fermion superconductor CeCoIn$$_5$$ by example

Sakai, Hironori

no journal, , 

In the heavy fermion superconductor CeCoIn$$_5$$, dilute substitutions by Sn or Cd suppress the superconductivity or induce an antiferromagnetically ordered state. Such impurity effects have been microscopically investigated by nuclear quadrupole resonance (NQR) technique. While the Sn substituents weaken electronic correlations and suppress the superconductivity, the Cd substituents induce local moments closely around themselves but the bulk electronic state far from the substituents stays as in a pure CeCoIn$$_5$$. Such a heterogeneous electronic state in the Cd substituted system means a local breakage of Kondo hybridization by non-magnetic Cd substituents.

Oral presentation

Local moments in the heterogeneous electronic state of Cd or Zn-substituted CeCoIn$$_5$$; Around Kondo holes

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Yokoyama, Makoto*; Zhu, J.-X.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

no journal, , 

We have used nuclear quadrupole resonance (NQR) to probe microscopically the response of a prototypical quantum critical metal CeCoIn$$_5$$ to substitutions of small amounts of Cd or Zn for In. Such non-magnetic Cd or Zn substitutions induce a long range antiferromagnetism. In the case of the Cd substitutions, approximately half of the Cd substituents induce local Ce moments in their close proximity, as observed by site-dependent longitudinal nuclear spin relaxation rates $$1/T_1$$. In the case of Zn substitutions, the similar site dependence of $$1/T_1$$ is observed as well. We will discuss about the heterogeneous electronic state realized in such a dilutely substituted system.

Oral presentation

NQR/NMR study on Zn-doped CeCoIn$$_5$$

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ronning, F.*; Zhu, J.-X.*; Suzuki, Kohei*; Oshima, Yoshiki*; Yokoyama, Makoto*

no journal, , 

Dilute substitutions of non-magnetic dopants Zn can induce a long-ranged antiferromagnetic ordering to a heavy fermion superconductor CeCoIn$$_5$$. We have microscopically investigated the Zn-doped CeCoIn$$_5$$ by means of the nuclear quadrupole/magnetic resonance (NQR/NMR) techniques.

Oral presentation

NQR/NMR study of Zn-doped CeCoIn$$_5$$

Sakai, Hironori; Hattori, Taisuke; Higa, Nonoka; Tokunaga, Yo; Kambe, Shinsaku; Ronning, F.*; Zhu, J.-X.*; Suzuki, Kohei*; Oshima, Yoshiki*; Yokoyama, Makoto*

no journal, , 

We have used Nuclear Quadrupole Resonance (NQR) to probe microscopically the response of prototypical quantum critical metal CeCoIn$$_5$$ to substitutions of small amounts of Cd or Zn for In. Such non-magnetic Cd or Zn substitutions induce a long range antiferromagnetism. In the case of Cd substitutions, approximately half of the Cd substituents induce local Ce moments in their close proximity, as observed by site-dependent longitudinal nuclear spin relaxation rates $$1/T_1$$. In the paramagnetic state, the values of $$1/T_1$$ at the main peak position are similar to those in the pure CeCoIn$$_5$$, while those are enhanced at the skirt position of spectrum. We will discuss about the heterogeneous electronic state realized in such a Zn substituted system and discuss about the coexistence of superconductivity with the antiferromagnetism, as well.

Oral presentation

NMR/NQR study for substitution effect in a antiferromagnetic quantum critical metal CeCoIn$$_5$$

Sakai, Hironori

no journal, , 

We have performed NMR/NQR experiments for slightly substituted CeCoIn$$_5$$ by several substituents of Cd, Zn and Ni. In this presentation, the microscopic electronic states will be discussed.

Oral presentation

Microscopic study of Ni and Zn substitution effects in heavy fermion superconductor CeCoIn$$_5$$

Sakai, Hironori; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Ronning, F.*; Zhu, J.-X.*; Thompson, J. D.*; Kotegawa, Hisashi*; To, Hideki*; Suzuki, Kohei*; et al.

no journal, , 

Heavy fermion superconductor CeCoIn$$_5$$ is considered as a quantum critical antiferromagnetic material. When the In elements are slightly substituted by Zn elements, a long-range antiferromagnetism is induced. On the other hand, slight Sn substitutions make the system step away from the quantum critical point. In the case of Zn substitutions, heterogeneity of antiferromagnetic area in the matrix of heavy fermion state has been microscopically confirmed by NQR measurements. In the case of Ni substitutions for the Co elements, the NQR result appears to be the same as in Sn substituted system.

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