Haga, Yoshinori; Opletal, P.; Tokiwa, Yoshifumi; Yamamoto, Etsuji; Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori
Journal of Physics; Condensed Matter, 34(17), p.175601_1 - 175601_7, 2022/04
Tokunaga, Yo; Sakai, Hironori; Kambe, Shinsaku; Haga, Yoshinori; Tokiwa, Yoshifumi; Opletal, P.; Fujibayashi, Hiroyuki*; Kinjo, Katsuki*; Kitagawa, Shunsaku*; Ishida, Kenji*; et al.
Journal of the Physical Society of Japan, 91(2), p.023707_1 - 023707_5, 2022/02
Te NMR experiments in field () applied along the easy magnetization axis (the -axis) revealed slow electronic dynamics developing in the paramagnetic state of UTe. The observed slow fluctuations are concerned with a successive growth of long-range electronic correlations below 3040 K, where the spin susceptibility along the hard magnetization axis (the -axis) shows a broad maximum. The experiments also imply that tiny amounts of disorder or defects locally disturb the long-range electronic correlations and develop an inhomogeneous electronic state at low temperatures, leading to a low temperature upturn observed in the bulk-susceptibility in . We suggest that UTe would be located on the paramagnetic side near an electronic phase boundary, where either the magnetic or Fermi-surface instability would be the origin of the characteristic fluctuations.
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 is known to be induced by slight substitutions of non-magnetic Zn atoms for In. In nominally 7% Zn substituted CeCoIn, an antiferromagnetic (AFM) state coexists with heavy fermion superconductivity. Heterogeneity of the electronic states is investigated in Zn doped CeCoIn by means of nuclear quadrupole and magnetic resonances (NQR and NMR). Site-dependent NQR relaxation rates 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 . At lower temperatures, an anisotropic superconducting (SC) gap below the SC transition temperature , 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.
Sakai, Hironori; Matsumoto, Yuji*; Haga, Yoshinori; Tokunaga, Yo; Kambe, Shinsaku
Physical Review B, 103(8), p.085114_1 - 085114_8, 2021/02
The microscopic origin of a magnetic phase diagram under pressure in a heavy fermion antiferromagnet CeRhSi was investigated using the Si nuclear magnetic resonance (NMR) technique. We investigated the temperature and pressure dependencies of -independent local fluctuations caused by the single-site Kondo effect. A universal scaling behavior observed on the energy scale of the local fluctuations in an entire pressure region demonstrates that a characteristic energy scale of Kondo interactions monotonically increases by applying pressure without a critical anomaly around the quantum critical pressure of antiferromagnetism. Our NMR result agrees with the Doniach picture of the heavy-fermion phase diagram, where the progressive delocalization of the -electrons occurs across , accompanied by the development of antiferromagnetic correlations among the -electrons.
Sakai, Hironori; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Ramakrishna, S. K.*; Reyes, A. P.*; Rosa, P. F. S.*; Ronning, F.*; Thompson, J. D.*; Fisk, Z.*; et al.
JPS Conference Proceedings (Internet), 30, p.011169_1 - 011169_6, 2020/03
Uranium disulfide -US showing a semimetal-to-semiconductor crossover has been investigated by the nuclear magnetic resonance (NMR) technique for S nuclei with the nuclear spin of . Since the natural concentration 0.76% of NMR active S nuclei is too dilute, the isotopic enrichment to 50% has been carried out for the single crystal growth. The S NMR spectra have been successfully obtained using a single crystal of -US with external fields along the crystallographic axis. The S sites assignments have been made based on these NMR spectra.
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
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
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
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.
Radioisotopes, 67(8), p.389 - 401, 2018/08
no abstracts in English
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
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.
Pospil, J.*; Haga, Yoshinori; Kohama, Yoshimitsu*; Miyake, Atsushi*; Kambe, Shinsaku; Tateiwa, Naoyuki; Valika, M.*; Proschek, P.*; Prokleka, J.*; Sechovsk, V.*; et al.
Physical Review B, 98(1), p.014430_1 - 014430_7, 2018/07
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
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
High 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
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
Al 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
In 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
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.
Sakai, Hironori; Ronning, F.*; Hattori, Takanori; Tokunaga, Yo; Kambe, Shinsaku; Zhu, J.-X.*; Wakeham, N.*; Yasuoka, Hiroshi; Bauer, E. D.*; Thompson, J. D.*
Journal of Physics; Conference Series, 807(3), p.032001_1 - 032001_6, 2017/04
We have used nuclear quadrupole resonance (NQR) to probe microscopically the response of a prototypical quantum critical metal CeCoIn to substitutions of small amounts of Cd for In. Approximately half of the Cd substituents induce local Ce moments in their close proximity, as observed by site-dependent longitudinal nuclear spin relaxation rates . To reaffirm that localized moments are induced around the Cd substituents, we find a Gaussian spin-echo decay rate of transverse nuclear spin relaxation. Further, for the NQR subpeak is found to be proportional to temperatures, again indicating local moments fluctuations around the Cd substituents, while that for the NQR main peak shows a -dependence. The latter temperature dependence is close to 0.75 in pure CeCoIn and indicates that the bulk electronic state is located close to a two dimensional quantum critical instability.
Pospisil, J.; Gochi, Jun*; Haga, Yoshinori; Honda, Fuminori*; Uwatoko, Yoshiya*; Tateiwa, Naoyuki; Kambe, Shinsaku; Nagasaki, Shoko*; Homma, Yoshiya*; Yamamoto, Etsuji
Journal of the Physical Society of Japan, 86(4), p.044709_1 - 044709_6, 2017/04