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Journal Articles

$$^{125}$$Te-NMR study on a single crystal of heavy fermion superconductor UTe$$_2$$

Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Hattori, Taisuke; Higa, Nonoka; Nakamine, Genki*; Kitagawa, Shunsaku*; Ishida, Kenji*; Nakamura, Ai*; Shimizu, Yusei*; et al.

Journal of the Physical Society of Japan, 88(7), p.073701_1 - 073701_4, 2019/07

 Times Cited Count:29 Percentile:95.25(Physics, Multidisciplinary)

We report $$^{125}$$Te-NMR studies on a newly discovered heavy fermion superconductor UTe$$_2$$. Using a single crystal, we have measured the $$^{125}$$Te-NMR Knight shift $$K$$ and spin-lattice relaxation rate $$1/T_1$$ for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static ($$K$$) and dynamical susceptibilities ($$1/T_1$$) in the paramagnetic state above about 20 K. Around 20 K, however, we have observed a sudden loss of NMR spin-echo signal due to sudden enhancement of the NMR spin-spin relaxation rate $$1/T_2$$, when the field is applied along the easy axis of magnetization (=$$a$$ axis). This behavior suggests the development of longitudinal magnetic fluctuations along the $$a$$ axis at very low frequencies below 20 K.

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:3 Percentile:33.95(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

Occupation sites and valence states of Co dopants in (La, Co)-codoped M-type Sr ferrite; $$^{57}$$Fe and $$^{59}$$Co nuclear magnetic resonance studies

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ueda, Hiroaki*; Tanioku, Yasuaki*; Michioka, Chishiro*; Yoshimura, Kazuyoshi*; Takao, Kenta*; Shimoda, Aiko*; et al.

Physical Review B, 98(6), p.064403_1 - 064403_10, 2018/08

 Times Cited Count:6 Percentile:45.58(Materials Science, Multidisciplinary)

To specify preferential occupation sites of Co substituents and to clarify charge and spin states of Co ions in (La, Co)-cosubstituted hexagonal magnetoplumbite-type (M-type) Sr ferrite, $$^{57}$$Fe and $$^{59}$$Co nuclear magnetic resonance (NMR) spectra are measured under zero and external magnetic fields using powdered and single crystalline specimens. To a considerable degree, the charge compensation between La$$^{3+}$$ and Co$$^{2+}$$ works in the equal (La, Co)-codoped case, where more than half of the Co ions are considered to be present in the minority spin $$4f_1$$ sites at the center of the oxygen tetrahedra, with the $$S$$ = 3/2 state carrying a small orbital moment owing to spin-orbit interaction. The remaining small number of high-spin Co$$^{2+}$$ ($$S$$ = 3/2, $$L$$ = 1) ions with unquenched orbital moments would be distributed to the other octahedral $$12k$$, $$2a$$, and $$4f_2$$ sites.

Journal Articles

Easy-plane XY spin fluctuations in the cycloidal magnet UPtGe studied via field orientation-dependent $$^{195}$$Pt NMR

Tokunaga, Yo; Nakamura, Ai*; Aoki, Dai*; Shimizu, Yusei*; Homma, Yoshiya*; Honda, Fuminori*; Sakai, Hironori; Hattori, Taisuke; Kambe, Shinsaku

Physical Review B, 98(1), p.014425_1 - 014425_5, 2018/07

 Times Cited Count:1 Percentile:8.26(Materials Science, Multidisciplinary)

$$^{195}$$Pt NMR measurements have been performed on a single crystal of the uranium-based compound UPtGe, which is the only 5f system known to possess an incommensurate helical (cycloidal) structure below TN = 50 K. Knight shift measurement confirmed the isotropic character of the static spin susceptibilities in hexagonal-like ac crystal planes of the EuAuGe-type crystal structure. The hyperfine coupling constants were also found to be isotropic in the planes. Nuclear relaxation rate measurement revealed the development of the antiferro-magnetic spin fluctuations with XY character confined to the hexagonal-like plane below 200 K. The results present a clear contrast to the Ising anisotropy of the fluctuations in ferromagnetic superconductors UCoGe and URhGe.

Journal Articles

Odd-parity electronic multipolar ordering in URu$$_2$$Si$$_2$$; Conclusions from Si and Ru NMR measurements

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Higa, Nonoka; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*; Harima, Hisatomo*

Physical Review B, 97(23), p.235142_1 - 235142_10, 2018/06

AA2018-0180.pdf:1.09MB

 Times Cited Count:16 Percentile:77.41(Materials Science, Multidisciplinary)

Journal Articles

Ruderman-Kittel interaction between Si in URu$$_{2}$$Si$$_{2}$$

Kambe, Shinsaku; Hattori, Taisuke; Tokunaga, Yo; Sakai, Hironori; Matsuda, Tatsuma*; Haga, Yoshinori; Walstedt, R. E.*

Journal of Physics; Conference Series, 969(1), p.012033_1 - 012033_6, 2018/03

 Times Cited Count:1 Percentile:64.34

High quality URu$$_{2}$$Si$$_{2}$$ enriched in $$^{29}$$Si isotope, which is an NMR nucleus, by 52% was prepared. Since the natural abundance ratio of $$^{29}$$Si isotope is about 4%, the accumulated measurement time can be shortened to about one hundredth by this concentration. Results of the Si-NMR linewidth of hidden ordered phase using this single crystal sample have already been reported. In this report, we will report more detailed analysis on the magnetic field, temperature and angle of this line width We also discuss the possibility of distribution of magnetic susceptibility in two-fold symmetry by RKKY model.

Journal Articles

Evidence for spin singlet pairing with strong uniaxial anisotropy in URu$$_2$$Si$$_2$$ using nuclear magnetic resonance

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Matsuda, Tatsuma*; Haga, Yoshinori

Physical Review Letters, 120(2), p.027001_1 - 027001_5, 2018/01

 Times Cited Count:10 Percentile:72.43(Physics, Multidisciplinary)

Journal Articles

Anisotropy of spin fluctuations in a tetragonal heavy fermion antiferromagnet CeRhAl$$_4$$Si$$_2$$

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ghimire, N. J.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Journal of Physics; Conference Series, 868(1), p.012012_1 - 012012_5, 2017/07

 Times Cited Count:1 Percentile:57.57

$$^{27}$$Al NMR experiments have been performed using a single crystal of CeRhAl$$_4$$Si$$_2$$. In the paramagnetic state, Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which has a local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. The relaxation rates suggest that 4$$f$$ electrons behave as local moments in the high temperatures. From the NMR spectral analyses, the antiferromagnetic structures are discussed.

Journal Articles

Nature of distributed two-fold ordering in URu$$_2$$Si$$_2$$

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Walstedt, R. E.*

Journal of Physics; Conference Series, 868(1), p.012003_1 - 012003_7, 2017/07

BB2015-1834.pdf:0.47MB

 Times Cited Count:0 Percentile:0.04

In the hidden-ordered state of URu$$_2$$Si$$_2$$, a modest breaking of the fourfold symmetry was suggested in previous $$^{29}$$Si NMR basal-plane field rotation measurements. Based on the detail analysis of $$^{29}$$Si NMR linewidth, the occurrence of a distribution of twofold local fields at the Si sites is suggested even in a high-quality single crystal. A possible picture for the distributed two-fold ordering will be discussed.

Journal Articles

$$T$$ dependence of nuclear spin-echo decay at low temperatures in YbRh$$_2$$Si$$_2$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Hattori, Taisuke; Lapertot, G.*; Matsuda, Tatsuma*; Knebel, G.*; Flouquet, J.*; Walstedt, R. E.*

Physical Review B, 95(19), p.195121_1 - 195121_8, 2017/05

AA2017-0083.pdf:0.74MB

 Times Cited Count:3 Percentile:23.04(Materials Science, Multidisciplinary)

The authors report $$^{29}$$Si nuclear spin-echo oscillations and decay measurements on a single crystal of YbRh$$_2$$Si$$_2$$. These quantities are found to be $$T$$ independent from 300 K down to $$sim$$20 K, showing, however, a strong $$T$$ dependence below 20 K. These results indicate that electronic states near the Fermi level are modified at low temperatures. The observed spin-echo oscillations can be interpreted with the Ruderman-Kittel and pseudo-dipolar interactions between nearest-neighbor Si nuclei driven by conduction electron scattering at the Fermi surface. Possible modifications to the Fermi surface at low temperatures are discussed.

Journal Articles

No detectable change in in-plane $$^{29}$$Si knight shift in the superconducting state of URu$$_2$$Si$$_2$$

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Matsuda, Tatsuma*; Haga, Yoshinori

Journal of the Physical Society of Japan, 85(7), p.073711_1 - 073711_4, 2016/07

 Times Cited Count:7 Percentile:56.08(Physics, Multidisciplinary)

Using a high-quality single crystal of URu$$_2$$Si$$_2$$, we performed $$^{29}$$Si Knight shift measurements with an applied magnetic field $$H^a$$ along the crystalline $$a$$ axis, i.e., along the magnetic hard axis, for temperatures down to 50 mK. The narrow, single-peak $$^{29}$$Si NMR spectrum obtained from this crystal allowed us to examine the temperature variation of the Knight shift $$K(T)$$, and hence, that of the variation of the spin susceptibility with sensitivity on the order of 0.001%. At this precision, no observable change in $$K(T)$$ was detected from 50 mK up to the superconducting transition at $$T_{rm SC}(H^a)sim$$ 1 K. Our results correspond to either an extremely small spin susceptibility in the hidden-order state along the magnetic hard axis or to possible spin-triplet superconductivity in this system.

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:12 Percentile:59.65(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

$$^{29}$$Si NMR spin-echo decay in YbRh$$_2$$Si$$_2$$

Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Hattori, Taisuke; Lapertot, G.*; Matsuda, Tatsuma*; Knebel, G.*; Flouquet, J.*; Walstedt, R. E.*

Journal of Physics; Conference Series, 683(1), p.012006_1 - 012006_7, 2016/02

BB2015-1546.pdf:0.87MB

 Times Cited Count:1 Percentile:60.83

By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time ($$T_1$$) measurements on a single crystal sample YbRh$$_2$$Si$$_2$$, the magnetic excitations around quantum critical phase transition is investigated. It is revealed that the coexisting Fermi and non-Fermi states appears near the quantum critical phase transition. Such a mottled state is considered to have remained hidden in Ce and U heavy fermion compounds, owing presumably to short lifetimes for the two states. The mottled state is highly anisotropic to applied magnetic field, which is consistent with previous studies. The origin of mottled state will be discussed.

Journal Articles

Incommensurate to commensurate antiferromagnetism in CeRhAl$$_4$$Si$$_2$$; An $$^{27}$$Al NMR study

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Ghimire, N. J.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

Physical Review B, 93(1), p.014402_1 - 014402_9, 2016/01

 Times Cited Count:1 Percentile:6.71(Materials Science, Multidisciplinary)

$$^{27}$$Al nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAl$$_4$$Si$$_2$$, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of $$T_{rm N1}$$=14 K and $$T_{rm N2}$$=9 K at zero external field. In the paramagnetic state, the Knight shifts, quadrupolar frequency, and asymmetric parameter of electrical field gradient on the Al sites have been determined, which have local orthorhombic symmetry. The transferred hyperfine coupling constants are also determined. Analysis of the NMR spectra indicates that a commensurate antiferromagnetic structure exists below $$T_{rm N2}$$, but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between $$T_{rm N1}$$ and $$T_{rm N2}$$. The spin-lattice relaxation rate suggests that the $$4f$$ electrons behave as local moments at temperatures above $$T_{rm N1}$$.

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

$$^{29}$$Si NMR study on single crystalline URu$$_2$$Si$$_2$$

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori

no journal, , 

Recently possible nematic order has been discussed with several experiments in so-called "hidden order" phase in URu$$_2$$Si$$_2$$. This makes the superconductivity in URu$$_2$$Si$$_2$$ a new interesting system where we can investigate the relationship between nematicity and superconductivity. This is because the chiral superconductivity, which breaks the time-reversal symmetry, under nematic order is suggested theoretically to show peculiar behavior, and the supercoducting pairing function in URu$$_2$$Si$$_2$$ is expected as the chiral $$d$$-wave. Thus we have performed $$^{29}$$Si NMR measurements on a single crystalline URu$$_2$$Si$$_2$$ sample with the $$^{29}$$Si isotope enriched to about 50%.

Oral presentation

$$^{57}$$Fe NMR study in La-Co substituted M-type Sr ferrite

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Shimoda, Aiko*; Waki, Takeshi*; Tabata, Yoshikazu*; Nakamura, Hiroyuki*

no journal, , 

Zero field NMR experiments on SrFe$$_{12}$$O$$_{19}$$ and Sr$$_{1-x}$$La$$_{x}$$Fe$$_{12-x}$$Co$$_{x}$$O$$_{19}$$ have been performed. The substitued Co sites will be discussed based on the NMR spectra.

Oral presentation

Isotopic enrichment of $$^{33}$$S to single crystals of uranium chalcogenide $$beta$$-US$$_2$$

Sakai, Hironori; Hattori, Taisuke; Tokunaga, Yo; Kambe, Shinsaku; Pospisil, J.; Tateiwa, Naoyuki; Yamamoto, Etsuji; Haga, Yoshinori

no journal, , 

$$beta$$-US$$_2$$ exhibits a large magnetoresistive effect but the mechanism is still identified. In order to investigate microscopically be means of nuclear magnetic resonance (NMR) technique, isotopic enrichment of NMR-active $$^{33}$$S has been performed. The physical properties on the single crystals will be discussed.

Oral presentation

NMR study on exotic superconductor UCoGe/URu$$_2$$Si$$_2$$

Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori

no journal, , 

Recently possible nematic order has been discussed with several experiments in so-called "hidden order" phase in URu$$_2$$Si$$_2$$. This makes the superconductivity in URu$$_2$$Si$$_2$$ a new interesting system where we can investigate the relationship between nematicity and superconductivity. This is because the chiral superconductivity, which breaks the time-reversal symmetry, under nematic order is suggested theoretically to show peculiar behavior, and the supercoducting pairing function in URu$$_2$$Si$$_2$$ is expected as the chiral $$d$$-wave. Thus we have performed $$^{29}$$Si NMR measurements on a single crystalline URu$$_2$$Si$$_2$$ sample with the $$^{29}$$Si isotope enriched to about 50%.

Oral presentation

Si-NMR linewidth in the hidden ordered state of URu$$_2$$Si$$_2$$

Kambe, Shinsaku; Tokunaga, Yo; Sakai, Hironori; Hattori, Taisuke; Walstedt, R. E.*

no journal, , 

$$^{29}$$Si enriched high quality URu$$_{2}$$Si$$_{2}$$ is made. $$^{29}$$Si-NMR linewidth is measured and analyzed in detail. A possible RKKY model for linewidth is discussed.

55 (Records 1-20 displayed on this page)