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Journal Articles

Multiharmonic vector rf voltage control for wideband cavities driven by vacuum tube amplifiers in a rapid cycling synchrotron

Tamura, Fumihiko; Sugiyama, Yasuyuki*; Yoshii, Masahito*; Yamamoto, Masanobu; Omori, Chihiro*; Nomura, Masahiro; Shimada, Taihei; Hasegawa, Katsushi*; Hara, Keigo*; Furusawa, Masashi*

Physical Review Accelerators and Beams (Internet), 22(9), p.092001_1 - 092001_22, 2019/09

Beam loading compensation in the rf cavities is a key for acceleration of high intensity beams in 3 GeV RCS of the J-PARC. Since we employ wideband magnetic alloy rf cavities for the J-PARC RCS and the wake voltage contains several harmonics, a multiharmonic beam loading compensation is required. The multiharmonic rf feedforward for the most important six harmonics is implemented in the existing low level rf (LLRF) control system, which has been working fairly well for acceleration of high intensity beams of up to 1 MW. However, we found the degradation of the performance for compensation of the feedforward with very high intensity beams. Therefore, a multiharmonic vector rf voltage control has been developed. The detail of system configuration, commissioning methodology, and beam test results using very high intensity beams are described. The beam loading by the 1~MW equivalent beam in the cavity is successfully compensated.

Journal Articles

Spinmotive force in the out-of-plane direction generated by spin wave excitations in an exchange-coupled bilayer element

Zhou, W.*; Seki, Takeshi*; Imamura, Hiroshi*; Ieda, Junichi; Takanashi, Koki*

Physical Review B, 100(9), p.094424_1 - 094424_5, 2019/09

Journal Articles

Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance

Tateiwa, Naoyuki; Haga, Yoshinori; Sakai, Hironori; Yamamoto, Etsuji

Physical Review B, 100(6), p.064413_1 - 064413_7, 2019/08

We report the novel critical behavior of magnetization in low carrier concentration systems UTeS and USeS that exhibit the large negative magnetoresistance around the ferromagnetic transition temperatures $$T_{rm C}$$ $$sim$$ 85 and 23 K, respectively. We determine the critical exponents, $$beta$$ for the spontaneous magnetization $$M_{rm s}$$, $$gamma$$ for the magnetic susceptibility $$chi$$, and $$delta$$ for the magnetization isotherm at $$T_{rm C}$$ with several analytical methods. The ferromagnetic states in UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical exponents in the two compounds are different from those in the three-dimensional Ising system. Similar exponents have been reported for the uranium ferromagnetic superconductors UGe$$_2$$ and URhGe. An important finding is that the novel critical phenomenon appears regardless of the charge carrier density or the degree of the itinerancy of the $$5f$$ electrons.

Journal Articles

Electronic states of EuCu$$_2$$Ge$$_2$$ and EuCu$$_2$$Si$$_2$$ studied by soft X-ray photoemission spectroscopy

Kawasaki, Ikuto; Fujimori, Shinichi; Takeda, Yukiharu; Yamagami, Hiroshi; Iha, Wataru*; Hedo, Masato*; Nakama, Takao*; Onuki, Yoshichika*

Physical Review B, 100(3), p.035111_1 - 035111_8, 2019/07

Journal Articles

High-pressure structure and electronic properties of YbD$$_{2}$$ to 34 GPa

Klotz, S.*; Casula, M.*; Komatsu, Kazuki*; Machida, Shinichi*; Hattori, Takanori

Physical Review B, 100(2), p.020101_1 - 020101_5, 2019/07

Ytterbium dihydride (YbH$$_{2}$$) shows a well-known transition at $$approx$$16 GPa from a CaH$$_{2}$$-type structure to a high-pressure (high-$$P$$) phase with Yb at hcp sites and unknown H-positions. Here, we report its complete structure determination by neutron diffraction at 34 GPa. Hydrogen(deuterium) is located at 2$$a$$ and 2$$d$$ positions of space group $$P6_{3}/mmc$$, thus forming a high-symmetry "collapsed" close-packed lattice. The transition is sluggish and can be seen as a transfer of 1/2 of the hydrogen atoms from strongly corrugated H-layers to interstitial sites of the Yb-lattice. We demonstrate by first-principles calculations that the transition is related to a change from a completely filled $$f$$-electron configuration to a fractional $$f$$-hole ($$approx$$0.25 h) occupation in the high-$$P$$ phase. The $$f$$ $$to$$ $$d$$ charge transfer closes the gap at the transition and leads to a metallic ground state with sizeable electron-phonon interaction involving out-of-plane vibrational modes of interstitial hydrogen.

Journal Articles

Universal $$frac{1}{3}$$-suppression of magnonic shot noise in diffusive insulating magnets

Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*

Physical Review B, 100(1), p.014406_1 - 014406_8, 2019/07

Extending a Boltzmann-Langevin theory to magnons, we show a universality of current-noise suppression in diffusive systems against the difference of quantum-statistical properties of bosons and fermions.

Journal Articles

Unraveling anomalous isotope effect on hydrogen diffusivities in fcc metals from first principles including nuclear quantum effects

Kimizuka, Hajime*; Ogata, Shigenobu*; Shiga, Motoyuki

Physical Review B, 100(2), p.024104_1 - 024104_9, 2019/07

The behavior of H isotopes in crystals is a fundamental and recurrent theme in materials physics. Especially, the information on H diffusion over a wide temperature range provides a critical insight into the quantum mechanical nature of the subject; however, this is not yet fully explored. From state-of-the-art ab initio calculations to treat both electrons and nuclei quantum mechanically, we found that the temperature dependence of H isotope diffusivities in face-centered-cubic (fcc) Pd has an unconventional "reversed S" shape on Arrhenius plots. Such irregular behavior is ascribed to the competition between different nuclear quantum effects with different temperature and mass dependencies, which leads to a peculiar situation, where the heavier tritium ($$^3$$H) diffuses faster than the lighter protium ($$^1$$H) in the limited temperature range of 80 - 400 K. This unveils the mechanism of anomalous crossovers between the normal and reversed isotope effects observed in the experiments at high and low temperatures.

Journal Articles

Laser control of magnonic topological phases in antiferromagnets

Nakata, Koki; Kim, S. K.*; Takayoshi, Shintaro*

Physical Review B, 100(1), p.014421_1 - 014421_9, 2019/07

We study the laser control of magnon topological phases induced by the Aharonov-Casher effect in insulating antiferromagnets (AFs). Using Floquet formalism, we study nonequilibrium magnon dynamics away from the adiabatic limit and its effect on topological phenomena. Our results provide a handle to control and design magnon topological properties in the insulating AF, and thus open a new door to "photonic magnonics".

Journal Articles

Quantum dynamics of hydrogen in the iron-based superconductor LaFeAsO$$_{0.9}$$D$$_{0.1}$$ measured with inelastic neutron spectroscopy

Yamaura, Junichi*; Hiraka, Haruhiro*; Iimura, Soshi*; Muraba, Yoshinori*; Bang, J.*; Ikeuchi, Kazuhiko*; Nakamura, Mitsutaka; Inamura, Yasuhiro; Honda, Takashi*; Hiraishi, Masatoshi*; et al.

Physical Review B, 99(22), p.220505_1 - 220505_6, 2019/06

Inelastic neutron scattering was performed for an iron-based superconductor, where most of D (deuterium) replaces oxygen, while a tiny amount goes into interstitial sites. By first-principle calculation, we characterize the interstitial sites for D (and for H slightly mixed) with four equivalent potential minima. Below the superconducting transition temperature Tc = 26 K, new excitations emerge in the range 5-15 meV, while they are absent in the reference system LaFeAsO$$_{0.9}$$F$$_{0.1}$$. The strong excitations at 14.5 meV and 11.1 meV broaden rapidly around 15 K and 20 K, respectively, where each energy becomes comparable to twice of the superconducting gap. The strong excitations are ascribed to a quantum rattling, or a band motion of hydrogen, which arises only if the number of potential minima is larger than two.

Journal Articles

Negative Te spin polarization responsible for ferromagnetic order in the doped topological insulator V$$_{0.04}$$(Sb$$_{1-x}$$Bi$$_{x}$$)$$_{1.96}$$Te$$_{3}$$

Ye, M.*; Xu, T.*; Li, G.*; Qiao, S.*; Takeda, Yukiharu; Saito, Yuji; Zhu, S.-Y.*; Nurmamat, M.*; Sumida, Kazuki*; Ishida, Yukiaki*; et al.

Physical Review B, 99(14), p.144413_1 - 144413_7, 2019/04

 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Asymmetric quantum shot noise in magnon transport

Nakata, Koki; Onuma, Yuichi*; Matsuo, Mamoru*

Physical Review B, 99(13), p.134403_1 - 134403_7, 2019/04

We study a frequency-dependent noise-to-current ratio for asymmetric, symmetric, and noncommutative current noise in a ferromagnetic insulating junction, and extract quantum-mechanical properties of magnon transport at low temperatures. We demonstrate that the noncommutative noise, which vanishes in the dc limit (i.e., a classical regime), increases monotonically as a function of frequency, and show that the noncommutative noise associated directly with quantum fluctuations of magnon currents breaks through the classical upper limit determined by the symmetric noise and realizes asymmetric quantum shot noise. Finally, we show that our theoretical predictions are within experimental reach with current device and measurement schemes while exploiting low temperatures. Our work provides a platform toward experimental access to quantum fluctuations of magnon currents.

Journal Articles

Novel critical behavior of magnetization in URhSi; Similarities to the uranium ferromagnetic superconductors UGe$$_2$$ and URhGe

Tateiwa, Naoyuki; Haga, Yoshinori; Yamamoto, Etsuji

Physical Review B, 99(9), p.094417_1 - 094417_12, 2019/03

 Percentile:100(Materials Science, Multidisciplinary)

We study the critical behavior of dc magnetization in the uranium ferromagnet URhSi around the ferromagnetic phase transition at $$T_{rm C}{,}{sim}{,}$$10 K. The critical exponent $$beta$$ for the spontaneous magnetization below $$T_{rm C}$$, $$gamma$$ for the magnetic susceptibility, and $$delta$$ for the magnetic isotherm at $$T_{rm C}$$ have been determined as $$beta$$ = 0.300 $$pm$$ 0.002, $$gamma$$ = 1.00 $$pm$$ 0.02, and $$delta$$ = 4.32 $$pm$$ 0.04 by the scaling analysis and the critical isotherm analysis. Magnetization has strong uniaxial magnetic anisotropy in the ferromagnetic state of URhSi. However, the universality class of the critical phenomenon does not belong to the 3D Ising system ($$beta$$ = 0.325, $$gamma$$ = 1.241, and $$delta$$ = 4.82). The obtained exponents in URhSi are similar to those in uranium ferromagnetic superconductors UGe$$_2$$ and URhGe. We discuss the static and dynamical magnetic properties of URhSi in comparison with those in UGe$$_2$$, URhGe and UCoGe.

Journal Articles

Magnetic and electrical properties of the ternary compound U$$_2$$Ir$$_3$$Si$$_5$$ with one-dimensional uranium zigzag chains

Li, D. X.*; Honda, Fuminori*; Miyake, Atsushi*; Homma, Yoshiya*; Haga, Yoshinori; Nakamura, Ai*; Shimizu, Yusei*; Maurya, A.*; Sato, Yoshiki*; Tokunaga, Masashi*; et al.

Physical Review B, 99(5), p.054408_1 - 054408_9, 2019/02

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

 Percentile:100(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

Manifestation of electron correlation effect in 5$$f$$ states of uranium compounds revealed by 4$$d$$-5$$f$$ resonant photoelectron spectroscopy

Fujimori, Shinichi; Kobata, Masaaki; Takeda, Yukiharu; Okane, Tetsuo; Saito, Yuji; Fujimori, Atsushi; Yamagami, Hiroshi; Haga, Yoshinori; Yamamoto, Etsuji; Onuki, Yoshichika*

Physical Review B, 99(3), p.035109_1 - 035109_5, 2019/01

 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

$$^{239}$$Pu nuclear magnetic resonance in the candidate topological insulator PuB$$_4$$

Dioguardi, A. P.*; Yasuoka, Hiroshi*; Thomas, S. M.*; Sakai, Hironori; Cary, S. K.*; Kozimor, S. A.*; Albrecht-Schmitt, T. E.*; Choi, H. C.*; Zhu, J.-X.*; Thompson, J. D.*; et al.

Physical Review B, 99(3), p.035104_1 - 035104_6, 2019/01

 Percentile:100(Materials Science, Multidisciplinary)

We present a detailed nuclear magnetic resonance (NMR) study of $$^{239}$$Pu in bulk and powdered single-crystal plutonium tetraboride (PuB$$_4$$), which has recently been investigated as a potential correlated topological insulator. The $$^{239}$$Pu NMR spectra are consistent with axial symmetry of the shift tensor showing for the first time that $$^{239}$$Pu NMR can be observed in an anisotropic environment and up to room temperature. The temperature dependence of the $$^{239}$$Pu shift, combined with a relatively long spin-lattice relaxation time ($$T_1$$), indicate that PuB$$_4$$ adopts a nonmagnetic state with gaplike behavior consistent with our density functional theory calculations. The temperature dependencies of the NMR Knight shift and $$T^{-1}$$ imply bulk gaplike behavior confirming that PuB$$_4$$ is a good candidate topological insulator.

Journal Articles

Spin correlations of quantum spin liquid and quadrupole-ordered states of Tb$$_{2+x}$$Ti$$_{2-x}$$O$$_{7+y}$$

Kadowaki, Hiroaki*; Wakita, Mika*; F${aa}$k, B.*; Ollivier, J.*; Kawamura, Seiko; Nakajima, Kenji; Lynn, J. W.*

Physical Review B, 99(1), p.014406_1 - 014406_12, 2019/01

Spin correlations of the frustrated pyrochlore oxide Tb$$_{2+x}$$Ti$$_{2-x}$$O$$_{7+y}$$ have been investigated by using inelastic neutron scattering on single-crystalline samples (x = -0.007, 0.000, and 0.003), which have the putative quantum-spin-liquid (QSL) or electric-quadrupolar ground states. Spin correlations, which are notably observed in nominally elastic scattering, show short-range correlations around $$Gamma$$ points, tiny antiferromagnetic Bragg scattering at L and $$Gamma$$ points, and pinch-point-type structures around $$Gamma$$ points. The short-range spin correlations were analyzed using a random-phase approximation (RPA) assuming the paramagnetic state and two-spin interactions among Ising spins. These analyses have shown that the RPA scattering intensity well reproduces the experimental data using temperature- and x-dependent coupling constants of up to tenth-neighbor site pairs. This suggests that no symmetry breaking occurs in the QSL sample and that a quantum treatment beyond the semiclassical RPA approach is required. Implications of the experimental data and the RPA analyses are discussed.

Journal Articles

Gapless magnetic excitation in a heavily electron-doped antiferromagnetic phase of LaFeAsO$$_{0.5}$$D$$_{0.5}$$

Tamatsukuri, Hiromu*; Hiraka, Haruhiro*; Ikeuchi, Kazuhiko*; Iimura, Soshi*; Muraba, Yoshinori*; Nakamura, Mitsutaka; Sagayama, Hajime*; Yamaura, Junichi*; Murakami, Yoichi*; Kuramoto, Yoshio*; et al.

Physical Review B, 98(17), p.174415_1 - 174415_6, 2018/11

AA2018-0436.pdf:0.85MB

 Times Cited Count:1 Percentile:100(Materials Science, Multidisciplinary)

Magnetic excitations in a heavily electron-doped antiferromagnet, LaFeAsO$$_{0.5}$$D$$_{0.5}$$, have been investigated using powder inelastic neutron scattering. Unlike other parent compounds of the iron-based superconductors, the magnetic excitation gap in LaFeAsO$$_{0.5}$$D$$_{0.5}$$ was not detected down to the lowest measured temperature of 4 K. This result can be understood as a result of quasi-isotropy within the ab plane, which is consistent with the band calculation result that the $$d_{xy}$$ orbital plays the dominant role in the magnetism of LaFeAsO$$_{0.5}$$H$$_{0.5}$$. In addition, the intensities of the magnetic excitations in this phase are much stronger than those in nondoped LaFeAsO. Even in the paramagnetic phase, the magnetic excitation in LaFeAsO$$_{0.5}$$D$$_{0.5}$$ persists. These results corroborate recent studies showing that the electron doping enhances the localized nature in this system.

Journal Articles

Evidence of a structural quantum critical point in (Ca$$_x$$Sr$$_{1-x}$$)$$_3$$Rh$$_4$$Sn$$_{13}$$ from a lattice dynamics study

Cheung, Y. W.*; Hu, Y. J.*; Imai, Masaki*; Tanioku, Yasuaki*; Kanagawa, Hibiki*; Murakawa, Joichi*; Moriyama, Kodai*; Zhang, W.*; Lai, K. T.*; Yoshimura, Kazuyoshi*; et al.

Physical Review B, 98(16), p.161103_1 - 161103_5, 2018/10

 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

New antiferromagnetic order with pressure-induced superconductivity in EuFe$$_2$$As$$_2$$

Ikeda, Shugo*; Tsuchiya, Yu*; Zhang, X.-W.*; Kishimoto, Shunji*; Kikegawa, Takumi*; Yoda, Yoshitaka*; Nakamura, Hiroki; Machida, Masahiko; Glasbrenner, J.*; Kobayashi, Hisao*

Physical Review B, 98(10), p.100502_1 - 100502_6, 2018/09

 Percentile:100(Materials Science, Multidisciplinary)

The interplay between magnetism and superconductivity is one of important subjects to investigate the pairing mechanism in novel superconductors. We have found new coexistence between an antiferromagnetic order in the Fe sublattice and superconductivity of the FeAs-based EuFe$$_2$$As$$_2$$ superconductor in the pressure range from 2.4 to 3.0 GPa by $$^{57}$$Fe nuclear forward scattering (NFS) using a single crystal sample. The magnetic state in the Fe sublattice changes to a new antiferromagnetic one with superconductivity from a stripe-type antiferromagnetic one observed in normal conducting state at 2.7 GPa. Below the superconducting transition temperature, the temperature dependence of $$^{57}$$Fe NFS spectra reveals that the new antiferromagnetic order develops with the superconductivity. This non-trivial coupling of two ordered states in EuFe$$_2$$As$$_2$$ under pressure demonstrates a new and intriguing relationship between magnetism and superconductivity in Fe-based superconductors.

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