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Journal Articles

Unveiling spin-dependent unoccupied electronic states of Co$$_{2}$$MnGe (Ga) film via Ge (Ga) $$L_{2,3}$$ absorption spectroscopy

Yoshikawa, Tomoki*; Antonov, V. N.*; Kono, Takashi*; Kakoki, Masaaki*; Sumida, Kazuki; Miyamoto, Koji*; Takeda, Yukiharu; Saito, Yuji; Goto, Kazuki*; Sakuraba, Yuya*; et al.

Physical Review B, 102(6), p.064428_1 - 064428_7, 2020/08

Journal Articles

Enhancement of domain-wall mobility detected by NMR at the angular momentum compensation temperature

Imai, Masaki; Chudo, Hiroyuki; Matsuo, Mamoru; Maekawa, Sadamichi; Saito, Eiji

Physical Review B, 102(1), p.014407_1 - 014407_5, 2020/07

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Self-learning hybrid Monte Carlo; A First-principles approach

Nagai, Yuki; Okumura, Masahiko; Kobayashi, Keita*; Shiga, Motoyuki

Physical Review B, 102(4), p.041124_1 - 041124_6, 2020/07

 Times Cited Count:0

no abstracts in English

Journal Articles

Two-parameter model for optimizing target beam distribution with an octupole magnet

Meigo, Shinichiro; Oi, Motoki; Fujimori, Hiroshi*

Physical Review Accelerators and Beams (Internet), 23(6), p.062802_1 - 062802_24, 2020/06

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

As hadron accelerators for such as the ADS and spallation neutron source achieve increasing beam power, damage to targets is becoming increasingly severe. To mitigate this damage, nonlinear beam optics based on octupole magnets is attractive. Nonlinear optics can decrease the beam-focusing hazard due to failure of the rastering magnet. As a side effect of nonlinear optics, the beam size is known to expand drastically compared with linear optics. Nonlinear effects have been studied via a simplified filament model that ignores beam-divergence spread at the octupole magnet. In this study, a new generalized model is proposed for application to an octupole magnet, regardless of the filament-model approximation. It is found that the transverse distribution obtained by beam tracking can be specified by the introduction of only two parameters, namely the normalized octupole strength of $$K^{*}_8$$ and the $$cot phi$$ of the phase advance. To achieve the two antagonistic requirements of reduction of the beam-peak density and minimization of the beam loss, the transverse distribution is surveyed for a large range of beam position. It is found that a bell-shaped distribution with $$K^{*}_8 sim$$ 1 and $$cot phi sim$$ 3 can satisfy requirements. This result is applied to beam transport in the spallation neutron source at J-PARC. The calculation result given by the present model shows good agreement with the experimental data, and the peak current density is reduced by 50% compared with the linear-optics case.

Journal Articles

Evidence for magnon-phonon coupling in the topological magnet Cu$$_{3}$$TeO$$_{6}$$

Bao, S.*; Cai, Z.*; Si, W.*; Wang, W.*; Wang, X.*; Shangguan, Y.*; Ma, Z.*; Dong, Z.-Y.*; Kajimoto, Ryoichi; Ikeuchi, Kazuhiko*; et al.

Physical Review B, 101(21), p.214419_1 - 214419_8, 2020/06

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

$$q$$=0 long-range magnetic order in centennialite CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O; A Spin-$$frac{1}{2}$$ perfect kagome antiferromagnet with $$J_{1}$$-$$J_{2}$$-$$J_{d}$$

Iida, Kazuki*; Yoshida, Hiroyuki*; Nakao, Akiko*; Jeschke, H. O.*; Iqbal, Y.*; Nakajima, Kenji; Kawamura, Seiko; Munakata, Koji*; Inamura, Yasuhiro; Murai, Naoki; et al.

Physical Review B, 101(22), p.220408_1 - 220408_6, 2020/06

Crystal and magnetic structures of the mineral centennialite CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O are investigated by means of synchrotron X-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. In CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O, Cu$$^{2+}$$ ions form a geometrically perfect kagome network with antiferromagnetic $$J_{1}$$. No intersite disorder between Cu$$^{2+}$$ and Ca$$^{2+}$$ ions is detected. CaCu$$_{3}$$(OD)$$_{6}$$Cl$$_{2}$$ $$cdot$$ 0.6D$$_{2}$$O enters a magnetic long-range ordered state below $$T_{rm N}$$ = 7.2 K, and the $$q$$=0 magnetic structure with negative vector spin chirality is obtained. The ordered moment at 0.3 K is suppressed to 0.58(2)$$mu$$B. Our DFT calculations indicate the presence of antiferromagnetic $$J_{2}$$ and ferromagnetic $$J_{d}$$ superexchange couplings of a strength which places the system at the crossroads of three magnetic orders (at the classical level) and a spin-$$frac{1}{2}$$ PFFRG analysis shows a dominance of $$q$$=0 type magnetic correlations, consistent with and indicating proximity to the observed $$q$$=0 spin structure. The results suggest that this material is located close to a quantum critical point and is a good realization of a $$J_{1}$$-$$J_{2}$$-$$J_{d}$$ kagome antiferromagnet.

Journal Articles

Magnetically induced electric polarization in Ba$$_{3}$$Fe$$_{2}$$O$$_{5}$$Cl$$_{2}$$ with tunable direction in three dimensions

Abe, Nobuyuki*; Shiozawa, Shunsuke*; Matsuura, Keisuke*; Sagayama, Hajime*; Nakao, Akiko*; Ohara, Takashi; Tokunaga, Yusuke*; Arima, Takahisa*

Physical Review B, 101(18), p.180407_1 - 180407_5, 2020/05

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Nuclear quantum effect for hydrogen adsorption on Pt(111)

Yan, L.*; Yamamoto, Yoshiyuki*; Shiga, Motoyuki; Sugino, Osamu*

Physical Review B, 101(16), p.165414_1 - 165414_9, 2020/04

Nuclear quantum effect and many-body interaction importantly interplay in the hydrogen on the Pt(111) system under the high coverage conditions of electrochemical interest, as revealed by our ab initio path integral and ring polymer molecular dynamics simulations done at room temperature. At the full monolayer coverage, hydrogen atoms are close-packed either at the atop sites or the fcc sites owing to their strong repulsion and the nearly degenerate nature of the adsorption sites. While at the 2/3 monolayer, they are delocalized over the fcc and hcp sites via the bridge sites because of the hopping. The quantum many-body effect is thus crucially important in determining the coverage dependence and provides a clue for reconciling the long-standing controversy on this system.

Journal Articles

Manipulation of saturation magnetization and perpendicular magnetic anisotropy in epitaxial Co$$_{x}$$Mn$$_{4-x}$$N films with ferrimagnetic compensation

Ito, Keita*; Yasutomi, Yoko*; Zhu, S.*; Nurmamat, M.*; Tahara, Masaki*; Toko, Kaoru*; Akiyama, Ryota*; Takeda, Yukiharu; Saito, Yuji; Oguchi, Tamio*; et al.

Physical Review B, 101(10), p.104401_1 - 104401_8, 2020/03

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Majorana corner flat bands in two-dimensional second-order topological superconductors

Kheirkhah, M.*; Nagai, Yuki; Chen, C.*; Marsiglio, F.*

Physical Review B, 101(10), p.104502_1 - 104502_9, 2020/03

 Times Cited Count:2 Percentile:7.53(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Self-learning Monte Carlo method with Behler-Parrinello neural networks

Nagai, Yuki; Okumura, Masahiko; Tanaka, Akinori*

Physical Review B, 101(11), p.115111_1 - 115111_12, 2020/03

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

no abstracts in English

Journal Articles

Crystal structure and magnetism of MnO under pressure

Klotz, S.*; Komatsu, Kazuki*; Polian, A.*; Machida, Shinichi*; Sano, Asami; Iti$'e$, J.-P.*; Hattori, Takanori

Physical Review B, 101(6), p.064105_1 - 064105_6, 2020/02

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Manganese oxide (MnO) is a prototype of an antiferromagnetic Mott-insulator. Here we investigate the interplay of magnetic ordering and lattice distortion across the N$'e$el temperature $$T_{N}$$ under pressure using neutron and X-ray diffraction. We find an increase of $$T_{N}$$ with a rate of $$T_{N}/dP$$ = +4.5(5) K/GPa, an increase of the rhombohedral distortion $$alpha$$ by $$dalpha/dP$$ = +0.018$$^{circ}$$/GPa, as well as a volume striction which is insensitive to pressure. These results allow to retrieve the dependence of the coupling constants $$J_{1}$$ and $$J_{2}$$ on interatomic distances and compare it to first-principles predictions. Antiferromagnetic diffuse scattering was observed up to $$sim$$1.2 $$T_{N}$$, and long-range magnetic order appears at room temperature at 42 GPa.

Journal Articles

Nematic and time-reversal breaking superconductivities coexisting with quadrupole order in a $$Gamma_3$$ system

Kubo, Katsunori

Physical Review B, 101(6), p.064512_1 - 064512_10, 2020/02

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Lattice dynamics in FeSe via inelastic X-ray scattering and first-principles calculations

Murai, Naoki; Fukuda, Tatsuo; Nakajima, Masamichi*; Kawamura, Mitsuaki*; Ishikawa, Daisuke*; Tajima, Setsuko*; Baron, A. Q. R.*

Physical Review B, 101(3), p.035126_1 - 035126_6, 2020/01

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

We report an inelastic X-ray scattering investigation of phonons in FeSe superconductor. Comparing the experimental phonon dispersion with density functional theory (DFT) calculations in the non-magnetic state, we found a significant disagreement between them. A better overall agreement was obtained by allowing for spin-polarization in DFT calculations, despite the absence of magnetic order in FeSe. This calculation gives a realistic approximation, at DFT level, of the disordered paramagnetic state of FeSe, in which strong spin fluctuations are present.

Journal Articles

Magnetic structures and quadratic magnetoelectric effect in LiNiPO$$_{4}$$ beyond 30 T

Fogh, E.*; Kihara, Takumi*; Toft-Petersen, R.*; Bartkowiak, M.*; Narumi, Yasuo*; Prokhnenko, O.*; Miyake, Atsushi*; Tokunaga, Masashi*; Oikawa, Kenichi; S${o}$rensen, M. K.*; et al.

Physical Review B, 101(2), p.024403_1 - 024403_12, 2020/01

 Times Cited Count:1 Percentile:21.49(Materials Science, Multidisciplinary)

Journal Articles

Development of a radio frequency quadrupole linac implemented with the equipartitioning beam dynamics scheme

Kondo, Yasuhiro; Morishita, Takatoshi; Jameson, R. A.*

Physical Review Accelerators and Beams (Internet), 22(12), p.120101_1 - 120101_8, 2019/12

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

Radio frequency quadrupole linac (RFQ) is the key component which realized modern high-current proton linacs, however, many RFQs are designed based on very conventional design schemes. We developed 3-MeV 50-mA H$$^-$$ (negative hydrogen) RFQ based on a beam space-charge physics concept. The equipartitioning scheme, which is widely used in the high intensity linac design, is implemented into the RFQ design. Design performances of 99.1% transmission, 0.24$$pi$$ mm mrad transverse normalized rms emittance, and 0.11$$pi$$ MeV deg for longitudinal direction are achieved with a vane length of 3 m and the final energy of 3 MeV. An RFQ employing this design concept was fabricated, and the design performance was confirmed by beam commissioning. In this paper, the design and result of the beam commissioning of this fully equipartitioned RFQ are described.

Journal Articles

Experimental investigation of the suppressed superconducting gap and double-resonance mode in Ba$$_{1-x}$$K$$_{x}$$Fe$$_{2}$$As$$_{2}$$

Ideta, Shinichiro*; Murai, Naoki; Nakajima, Masamichi*; Kajimoto, Ryoichi; Tanaka, Kiyohisa*

Physical Review B, 100(23), p.235135_1 - 235135_7, 2019/12

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

Journal Articles

Disorder-induced exceptional and hybrid point rings in Weyl/Dirac semimetals

Matsushita, Taiki*; Nagai, Yuki; Fujimoto, Satoshi*

Physical Review B, 100(24), p.245205_1 - 245205_9, 2019/12

 Times Cited Count:1 Percentile:68.36(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Element-specific density of states of Co$$_{2}$$MnGe revealed by resonant photoelectron spectroscopy

Kono, Takashi*; Kakoki, Masaaki*; Yoshikawa, Tomoki*; Wang, X.*; Sumida, Kazuki*; Miyamoto, Koji*; Muro, Takayuki*; Takeda, Yukiharu; Saito, Yuji; Goto, Kazuki*; et al.

Physical Review B, 100(16), p.165120_1 - 165120_6, 2019/10

 Times Cited Count:0 Percentile:100(Materials Science, Multidisciplinary)

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

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

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.

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