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Higa, Nonoka*; Ito, Takashi; Yogi, Mamoru*; Hattori, Taisuke; Sakai, Hironori; Kambe, Shinsaku; Guguchia, Z.*; Higemoto, Wataru; Nakashima, Miho*; Homma, Yoshiya*; et al.
Physical Review B, 104(4), p.045145_1 - 045145_7, 2021/07
Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)Lessux, G. G.*; Sakai, Hironori; Hattori, Taisuke*; Tokunaga, Yo; Kambe, Shinsaku; Kuhns, P. L.*; Reyes, A. P.*; Thompson, J. D.*; Pagliuso, P. G.*; Urbano, R. R.*
Physical Review B, 101(16), p.165111_1 - 165111_6, 2020/04
Times Cited Count:7 Percentile:45.15(Materials Science, Multidisciplinary)CeRhIn is a Kondo-lattice prototype in which a magnetic field 31T induces an abrupt Fermi-surface (FS) reconstruction and pronounced in-plane electrical transport anisotropy all within its antiferromagnetic state. Here we report low-temperature nuclear magnetic resonance (NMR) measurements revealing a pronounced decrease in the In formal Knight shift, without changes in crystal or magnetic structures, of CeRhIn at fields () spanning . We discuss the emergent state above in terms of a change in Ce's 4 orbitals that arises from field-induced evolution of crystal-electric field (CEF) energy levels. This change in orbital character enhances hybridization between the 4 and the conduction electrons that leads ultimately to an itinerant quantum-critical point at 50T.
Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, 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 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 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 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 , providing further support to the mechanism of superconductivity mediated by spin fluctuations in these materials.
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:56 Percentile:94.67(Physics, Multidisciplinary)We report Te-NMR studies on a newly discovered heavy fermion superconductor UTe. Using a single crystal, we have measured the Te-NMR Knight shift and spin-lattice relaxation rate for fields along the three orthorhombic crystal axes. The data confirm a moderate Ising anisotropy for both the static () and dynamical susceptibilities () 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 , when the field is applied along the easy axis of magnetization (= axis). This behavior suggests the development of longitudinal magnetic fluctuations along the axis at very low frequencies below 20 K.
Tokunaga, Yo; Orlova, A.*; Bruyant, N.*; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, 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 exhibits a field-induced anomaly associated with Fermi surface reconstruction at 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 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 . 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.
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:10 Percentile:46.45(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, Fe and 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 and Co 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 sites at the center of the oxygen tetrahedra, with the = 3/2 state carrying a small orbital moment owing to spin-orbit interaction. The remaining small number of high-spin Co ( = 3/2, = 1) ions with unquenched orbital moments would be distributed to the other octahedral , , and sites.
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:2 Percentile:10.5(Materials Science, Multidisciplinary)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.
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
Times Cited Count:19 Percentile:69.2(Materials Science, Multidisciplinary)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:53.12High quality URuSi enriched in Si isotope, which is an NMR nucleus, by 52% was prepared. Since the natural abundance ratio of 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.
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:12 Percentile:65.34(Physics, Multidisciplinary)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:49.82Al NMR experiments have been performed using a single crystal of CeRhAlSi. 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 electrons behave as local moments in the high temperatures. From the NMR spectral analyses, the antiferromagnetic structures are discussed.
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
Times Cited Count:0 Percentile:0.04In the hidden-ordered state of URuSi, a modest breaking of the fourfold symmetry was suggested in previous Si NMR basal-plane field rotation measurements. Based on the detail analysis of 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.
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
Times Cited Count:3 Percentile:17.22(Materials Science, Multidisciplinary)The authors report Si nuclear spin-echo oscillations and decay measurements on a single crystal of YbRhSi. These quantities are found to be independent from 300 K down to 20 K, showing, however, a strong 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.
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:49.16(Physics, Multidisciplinary)Using a high-quality single crystal of URuSi, we performed Si Knight shift measurements with an applied magnetic field along the crystalline axis, i.e., along the magnetic hard axis, for temperatures down to 50 mK. The narrow, single-peak Si NMR spectrum obtained from this crystal allowed us to examine the temperature variation of the Knight shift , 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 was detected from 50 mK up to the superconducting transition at 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.
Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, 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 () crystal plane. Our high-field 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 axis, while being unaffected by any field component along the axis. The observed close interplay between the SC and quantum fluctuations strongly supports a pairing mechanism mediated by these fluctuations in URhGe.
Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, 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:0.03Metamagnetism 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 URhCoGe and discuss the origin of the field induced superconducting phenomenon observed in high fields around 12 T.
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
Times Cited Count:1 Percentile:55.6By means of nuclear magnetic resonance (NMR) spin-lattice relaxation time () measurements on a single crystal sample YbRhSi, 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.
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:2 Percentile:10.73(Materials Science, Multidisciplinary)Al nuclear magnetic resonance (NMR) experiments have been performed on a single crystal of CeRhAlSi, which is an antiferromagnetic Kondo-lattice compound with successive antiferromagnetic transitions of =14 K and =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 , but an incommensurate modulation of antiferromagnetic moments is present in the antiferromagnetic state between and . The spin-lattice relaxation rate suggests that the electrons behave as local moments at temperatures above .
Tokunaga, Yo; Aoki, Dai*; Mayaffre, H.*; Krmer, S.*; Julien, M.-H.*; Berthier, C.*; Horvati, M.*; Hattori, Taisuke; Sakai, Hironori; Kambe, Shinsaku; et al.
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no abstracts in English
Hattori, Taisuke; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Haga, Yoshinori
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Recently possible nematic order has been discussed with several experiments in so-called "hidden order" phase in URuSi. This makes the superconductivity in URuSi 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 URuSi is expected as the chiral -wave. Thus we have performed Si NMR measurements on a single crystalline URuSi sample with the Si isotope enriched to about 50%.