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Journal Articles

Strong lattice anharmonicity exhibited by the high-energy optical phonons in thermoelectric material

Wu, P.*; Fan, F.-R.*; Hagihara, Masato*; Kofu, Maiko; Peng, K.*; Ishikawa, Yoshihisa*; Lee, S.*; Honda, Takashi*; Yonemura, Masao*; Ikeda, Kazutaka*; et al.

New Journal of Physics (Internet), 22(8), p.083083_1 - 083083_9, 2020/08

 Times Cited Count:2 Percentile:51.78(Physics, Multidisciplinary)

Thermoelectric material SnSe has aroused world-wide interests in the past years, and its inherent strong lattice anharmonicity is regarded as a crucial factor for its outstanding thermoelectric performance. However, the understanding of lattice anharmonicity in SnSe system remains inadequate, especially regarding how phonon dynamics are affected by this behavior. In this work, we present a comprehensive study of lattice dynamics on Na$$_{0.003}$$Sn$$_{0.997}$$Se$$_{0.9}$$S$$_{0.1}$$ by means of neutron total scattering, inelastic neutron scattering, Raman spectroscopy as well as frozen-phonon calculations. Lattice anharmonicity is evidenced by pair distribution function, inelastic neutron scattering and Raman measurements. By separating the effects of thermal expansion and multi-phonon scattering, we found that the latter is very significant in high-energy optical phonon modes. The strong temperature-dependence of these phonon modes indicate the anharmonicity in this system. Moreover, our data reveals that the linewidths of high-energy optical phonons become broadened with mild doping of sulfur. Our studies suggest that the thermoelectric performance of SnSe could be further enhanced by reducing the contributions of high-energy optical phonon modes to the lattice thermal conductivity via phonon engineering.

Journal Articles

Validating polarization effects in $$gamma$$-rays elastic scattering by Monte Carlo simulation

Omer, M.; Hajima, Ryoichi*

New Journal of Physics (Internet), 21(11), p.113006_1 - 113006_10, 2019/11

AA2019-0407.pdf:0.73MB

 Times Cited Count:4 Percentile:55.7(Physics, Multidisciplinary)

Journal Articles

Magnetic-impurity-induced modifications to ultrafast carrier dynamics in the ferromagnetic topological insulators Sb$$_{2-x}$$V$$_{x}$$Te$$_{3}$$

Sumida, Kazuki*; Kakoki, Masaaki*; Reimann, J.*; Nurmamat, M.*; Goto, Shinichi*; Takeda, Yukiharu; Saito, Yuji; Kokh, K. A.*; Tereshchenko, O. E.*; G$"u$dde, J.*; et al.

New Journal of Physics (Internet), 21(9), p.093006_1 - 093006_8, 2019/09

 Times Cited Count:6 Percentile:67.47(Physics, Multidisciplinary)

Journal Articles

Cesiated surface H$$^{-}$$ ion source; Optimization studies

Ueno, Akira

New Journal of Physics (Internet), 19(1), p.015004_1 - 015004_15, 2017/01

 Times Cited Count:8 Percentile:63.32(Physics, Multidisciplinary)

In order to satisfy the increasing intensity requirements of high-energy and high-intensity proton accelerators for an H$$_{-}$$ ion beam with small transverse normalized rms emittances of around 0.25 $$pi$$mm$$cdot$$mrad, diverse parameters possibly reducing the emittances were optimised. Such as the plasma electrode shape and temperature, the radio-frequency (RF) matching network for the igniter plasma, the filter-field strength and distribution, the strength of the axial magnetic field around the beam extraction hole, the cesiasion procedure and the cesium (Cs) density, impurity elements, and so on, were optimized with H$$_{-}$$ ion sources for the Japan Proton Accelerator Research Complex (J-PARC). By optimizing each parameter step by step, the J-PARC cesiated RF-driven H$$_{-}$$ ion source successfully produced the world brightest class beam with 95% beam transverse normalized rms emittances of 0.24 $$pi$$mm$$cdot$$mrad and an intensity of 66 mA.

Journal Articles

High order harmonics from relativistic electron spikes

Pirozhkov, A. S.; Kando, Masaki; Esirkepov, T. Z.; Gallegos, P.*; Ahmed, H.*; Ragozin, E. N.*; Faenov, A. Ya.*; Pikuz, T. A.*; Kawachi, Tetsuya; Sagisaka, Akito; et al.

New Journal of Physics (Internet), 16(9), p.093003_1 - 093003_30, 2014/09

 Times Cited Count:25 Percentile:81.51(Physics, Multidisciplinary)

Journal Articles

Microscopic properties of the heavy-fermion superconductor PuCoIn$$_5$$ explored by nuclear quadrupole resonance

Koutroulakis, G.*; Yasuoka, Hiroshi; Chudo, Hiroyuki; Tobash, P. H.*; Mitchell, J. N.*; Bauer, E. D.*; Thompson, J. D.*

New Journal of Physics (Internet), 16, p.053019_1 - 053019_12, 2014/05

 Times Cited Count:6 Percentile:49.45(Physics, Multidisciplinary)

We report $$^{115}$$In nuclear quadrupolar resonance (NQR) measurements on the heavy-fermion superconductor PuCoIn$$_5$$, in the temperature range 0.29 K $$leq Tleq$$75 K. The NQR parameters for the two crystallographically inequivalent In sites are determined, and their temperature dependence is investigated. A linear shift of the quadrupolar frequency with lowering temperature below the critical value $$T_c$$ is revealed, in agreement with the prediction for composite pairing. The nuclear spin-lattice relaxation rate $$T_1^{-1}(T)$$ clearly signals a superconducting (SC) phase transition at $$T_c simeq $$ 2.3 K, with strong spin fluctuations, mostly in-plane, dominating the relaxation process in the normal state near to $$T_c$$. Analysis of the $$T_1^{-1}$$ data in the SC state suggests that PuCoIn$$_5$$ is a strong-coupling $$d$$-wave superconductor.

Journal Articles

Generation and application of multi-path cat states of light

Ishida, Natsuko*; Ota, Yukihiro; Yamamoto, Yoshihisa*

New Journal of Physics (Internet), 11, p.033007_1 - 033007_15, 2009/03

 Times Cited Count:1 Percentile:11.58(Physics, Multidisciplinary)

We propose a scheme to generate a novel state, a multi-path cat state of light, in which $$N$$ photons are propagating in $$N$$ different paths. Starting with $$N$$ indistinguishable single-photon sources and using linear optical circuits, the target state is extracted with high fidelity. If a state preserving quantum non-demolition measurement of photon number can be incorporated into the generation scheme, the fidelity is further improved.

Journal Articles

Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors; An Anisotropic $$pm s$$-wave scenario

Nagai, Yuki*; Hayashi, Nobuhiko; Nakai, Noriyuki; Nakamura, Hiroki; Okumura, Masahiko; Machida, Masahiko

New Journal of Physics (Internet), 10(10), p.103026_1 - 103026_17, 2008/10

 Times Cited Count:75 Percentile:91.71(Physics, Multidisciplinary)

We discuss the nuclear magnetic relaxation rate and the superfluid density with the use of the effective five-band model by Kuroki et al (Phys. Rev. Lett. 101, 087004 (2008)) in Fe-based superconductors. We show that a fully gapped anisotropic $$pm$$s-wave superconductivity consistently explains experimental observations. In our phenomenological model, the gaps are assumed to be anisotropic on the electron-like $$beta$$ Fermi surfaces around the M point, where the maximum of the anisotropic gap is about four times larger than the minimum.

Journal Articles

Local electronic structure of Cr in the II-VI diluted ferromagnetic semiconductor Zn$$_{1-x}$$Cr$$_x$$Te

Kobayashi, Masaki*; Ishida, Yukiaki*; Hwang, J. I.*; Song, G. S.*; Fujimori, Atsushi; Yang, C. S.*; Lee, L.*; Lin, H.-J.*; Huang, D.-J.*; Chen, C. T.*; et al.

New Journal of Physics (Internet), 10, p.055011_1 - 055011_15, 2008/05

 Times Cited Count:13 Percentile:62.96(Physics, Multidisciplinary)

Journal Articles

Electronic properties of transuranium compounds with HoCoGa$$_5$$-type tetragonal crystal structure

Maehira, Takahiro*; Hotta, Takashi; Ueda, Kazuo*; Hasegawa, Akira*

New Journal of Physics (Internet), 8(2), p.24_1 - 24_20, 2006/02

 Times Cited Count:16 Percentile:66.17(Physics, Multidisciplinary)

By using a relativistic band-structrue calculation method, we investigate energy band structures and the Fermi surfaces of NpTGa$$_5$$, PuTGa$$_5$$, and AmCoGa$$_5$$ with transition metal atoms T. It is found in common that the energy bands in the vicinity of the Fermi level are mainly due to the large hybridization between $$5f$$ and Ga $$4p$$ electrons. For PuTGa$$_5$$, we observe several cylindrical sheets of Fermi surfaces with large volume for T=Co, Rh, and Ir. It is also found that the Fermi surfaces of NpFeGa$$_5$$, NpCoGa$$_5$$, and NpNiGa$$_5$$ are similar to those of UCoGa$$_5$$, UNiGa$$_5$$, and PuCoGa$$_5$$, respectively, except for small details. For AmCoGa$$_5$$, the Fermi surfaces are found to consist of large cylindrical electron sheets and small closed hole sheets, similar to PuCoGa$$_5$$. The similarity is basically understood by a rigid-band picture.

Journal Articles

An orbital-based scenario for the magnetic structure of neptunium compounds

Onishi, Hiroaki; Hotta, Takashi

New Journal of Physics (Internet), 6(1), p.193_1 - 193_16, 2004/12

We discuss a crucial role of orbital degree of freedom to understand the complex magnetic structure of actinide compounds from a microscopic viewpoint. Typical examples which we pick up here are UTGa$$_5$$ and NpTGa$$_5$$, where T denotes a transition metal ion. An orbital degenerate Hubbard model constructed from the $$j$$-$$j$$ coupling scheme is provided to investigate the magnetic structure of actinide compounds. By analyzing the model Hamiltonian with the use of unbiased numerical technique such as exact diagonalization, we obtain the phase diagram including several kinds of magnetic states. An orbital-based scenario is proposed to understand the change in the magnetic structure from G- to A-type antiferromagntic (AF) phases, experimentally observed in UNiGa$$_5$$ and UPtGa$$_5$$. We also discuss the appearance of three kinds of AF phases, C-, A-, and G-type, for NpTGa$$_5$$ (T=Fe, Co, and Ni).

Journal Articles

Slablike ion temperature gradient driven mode in reversed shear tokamaks

Idomura, Yasuhiro; Tokuda, Shinji; Kishimoto, Yasuaki

New Journal of Physics (Internet), 4(1), p.101.1 - 101.13, 2002/12

The ion temperature gradient driven (ITG) mode in reversed shear tokamaks is analyzed using a gyrokinetic toroidal particle code. It is found that the ITG mode in the reversed shear configuration shows a coupled mode structure between the slab and toroidal ITG modes. Especially in the $$q_{min}$$ region, a slab like feature due to the reversed shear slab ITG mode becomes strong. This coupled eigenmode structure is changed from a slab mode to a toroidal mode depending on $$eta_i=L_n/L_{ti}$$ and $$L_{ti}$$. Results show that in reversed shear tokamaks, the ITG mode is determined from a competition between the slab and toroidal ITG modes.

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