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Zhang, D.*; Hu, X.*; Chen, T.*; Abernathy, D. L.*; 梶本 亮一; 中村 充孝; 古府 麻衣子; Foley, B. J.*; Yoon, M.*; Choi, J. J.*; et al.
Physical Review B, 102(22), p.224310_1 - 224310_10, 2020/12
The long carrier lifetime and defect tolerance in metal halide perovskites (MHPs) are major contributors to the superb performance of MHP optoelectronic devices. Large polarons were reported to be responsible for the long carrier lifetime. Yet microscopic mechanisms of the large polaron formation, including the so-called phonon melting, are still under debate. Here, time-of-flight inelastic neutron scattering experiments and first-principles density-functional theory calculations were employed to investigate the lattice vibrations (or phonon dynamics) in methylammonium lead iodide, a prototypical example of MHPs. Our findings are that optical phonons lose temporal coherence gradually with increasing temperature which vanishes at the orthorhombic-to-tetragonal structural phase transition. Surprisingly, however, we found that the spatial coherence is still retained throughout the decoherence process. We argue that the temporally decoherent and spatially coherent vibrations contribute to the formation of large polarons in this metal halide perovskite.
金子 耕士; Cheung, Y. W.*; Hu, Y.*; 今井 正樹*; 谷奥 泰明*; 金川 響*; 村川 譲一*; 森山 広大*; Zhang, W.*; Lai, K. T.*; et al.
JPS Conference Proceedings (Internet), 30, p.011032_1 - 011032_6, 2020/03
A quantum critical point appears as a second-order phase transition which takes place at zero temperature. In contrast to heavy-fermion systems in which magnetism often plays a vital role, recent studies revealed that structural instabilities can drive a system to a quantum critical point as well. In quasi-skutterudite (Ca,Sr)Sn
(
=Rh, Ir), Sr
Ir
Sn
exhibits superconductivity around
5 K and a structural transition at
147 K. Applying physical or chemical pressure on Sr
Ir
Sn
suppresses
rapidly, and a quasi-linear
dependence of electrical resistivity, signature of non-Fermi liquid behavior, was observed where
extrapolates to 0 K. The isomorphs (Ca
Sr
)
Rh
Sn
exhibits similar behavior, where the criticality can be reached by
0.9 without external pressure. Neutron scattering experiments in Sr
Ir
Sn
evidences the second order nature of the structural transition at
by the observation of a continuous evolution of superlattice peak below
and a gradual increase of critical scattering upon approaching to
by cooling. Increase of
in (Ca
Sr
)
Rh
Sn
toward the quantum critical point leads to the systematic variation of the critical exponents of the order parameter. In addition, this substitution induces the phonon softening around the M point towards zero energy revealed by inelastic X-ray scattering experiment. We will present systematic variations in both elastic and inelastic channels upon approaching to the quantum critical point.
伊藤 啓太*; 安富 陽子*; Zhu, S.*; Nurmamat, M.*; 田原 昌樹*; 都甲 薫*; 秋山 了太*; 竹田 幸治; 斎藤 祐児; 小口 多美夫*; et al.
Physical Review B, 101(10), p.104401_1 - 104401_8, 2020/03
被引用回数:1 パーセンタイル:31.73(Materials Science, Multidisciplinary)Spintronics devices utilizing a magnetic domain wall motion have attracted increasing attention, and ferrimagentic materials with almost compensated magnetic moments are highly required to realize the fast magnetic domain wall motion. Here, we report a key function for this purpose in anti-perovskite CoMn
N films. Perpendicular magnetization emerges for
, and the saturation magnetization reaches a minimum value at
.
Ghys, L.*; Andreyev, A. N.; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; Cocolios, T. E.*; Cubiss, J.*; Derkx, X.*; et al.
Physical Review C, 100(5), p.054310_1 - 054310_13, 2019/11
被引用回数:5 パーセンタイル:18.92(Physics, Nuclear)The aim of this work was to investigate the -decay properties of
Fr and daughter products. Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Due to the very high statistics and the high beam purity, improved decay data for
Fr and its daughters were obtained. The observation of crossover transitions positioned the isomeric high-spin level of
At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of
At and 52(3) ms for the ground-state decay of
Fr.
Barzakh, A. E.*; Cubiss, J. G.*; Andreyev, A. N.; Seliverstov, M. D.*; Andel, B.*; Antalic, S.*; Ascher, P.*; Atanasov, D.*; Beck, D.*; Biero, J.*; et al.
Physical Review C, 99(5), p.054317_1 - 054317_9, 2019/05
被引用回数:3 パーセンタイル:27.46(Physics, Nuclear)Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in At have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope
At has been found to be larger than the average.
Ye, M.*; Xu, T.*; Li, G.*; Qiao, S.*; 竹田 幸治; 斎藤 祐児; Zhu, S.-Y.*; Nurmamat, M.*; 角田 一樹*; 石田 行章*; et al.
Physical Review B, 99(14), p.144413_1 - 144413_7, 2019/04
被引用回数:5 パーセンタイル:43.12(Materials Science, Multidisciplinary)We investigate the microscopic origin of ferromagnetism coupled with topological insulators in V-doped (Sb,Bi)Te
employing X-ray magnetic circular dichroism and angle-resolved two-photon photoemission spectroscopies, combined with first-principles calculations. We found an magnetic moment at the Te site anti-parallel to that of the V and Sb sites, which plays a key role in the ferromagnetic order. We ascribe it to the hybridization between Te 5
and V 3
majority spin states at the Fermi energy, consistent with the Zener-type
-
exchange interaction scenario. The substitution of Bi for Sb suppresses the bulk ferromagnetism by introducing extra electron carriers in the majority spin channel of the Te
states that compensates the antiparallel magnetic moment on the Te site. Our findings reveal important clues to designing magnetic topological insulators with higher Curie temperature that work under ambient conditions.
北里 宏平*; Milliken, R. E.*; 岩田 隆浩*; 安部 正真*; 大竹 真紀子*; 松浦 周二*; 荒井 武彦*; 仲内 悠祐*; 中村 智樹*; 松岡 萌*; et al.
Science, 364(6437), p.272 - 275, 2019/04
被引用回数:86 パーセンタイル:0.14(Multidisciplinary Sciences)小惑星探査機はやぶさ2のターゲット天体であるリュウグウは、始原的な炭素質物質で構成されていると考えられている。はやぶさ2に搭載された近赤外分光計(NIRS3)によって、天体の表面組成を得た。天体全体の観測で、弱く細い吸収が2.72ミクロンに確認され、OHを含む鉱物の存在を示している。弱いOH吸収と低いアルベドは熱やショックによって変質を受けた炭素質コンドライトに似ている。OHバンドの位置はほとんど一定であり、衝撃片の集合によって形成されたリュウグウは組成的に均質であることを示している。
Dioguardi, A. P.*; 安岡 弘志*; Thomas, S. M.*; 酒井 宏典; 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
被引用回数:0 パーセンタイル:100(Materials Science, Multidisciplinary)正方晶プルトニウムボロン化合物PuBの単結晶、および粉末試料を用いて、
Pu核核磁気共鳴(NMR)実験を行なった。この化合物は、最近になって強相関電子系のトポロジカル絶縁体候補物質と考えられている。
Pu核NMRスペクトルは、結晶内Pu位置の局所対称性を反映したものとなっており、NMRシフトとNMR緩和率の温度依存性は、エネルギーギャップをもつ非磁性状態にあることが示唆された。これは、密度汎関数理論計算結果とも矛盾しない。実際に観測された巨視的なギャップ状態は、本化合物がトポロジカル絶縁体候補であることを支持している。
Cheung, Y. W.*; Hu, Y. J.*; 今井 正樹*; 谷奥 泰明*; 金川 響*; 村川 譲一*; 森山 広大*; Zhang, W.*; Lai, K. T.*; 吉村 一良*; et al.
Physical Review B, 98(16), p.161103_1 - 161103_5, 2018/10
被引用回数:5 パーセンタイル:47.75(Materials Science, Multidisciplinary)Approaching a quantum critical point has been an effective route to stabilize superconductivity. While the role of magnetic QCPs has been extensively discussed, similar exploration of a structural QCP is scarce. Using inelastic X-ray scattering, we examine the phonon spectrum of the nonmagnetic quasi-skutterudite (CaSr
)
Rh
Sn
, which represents a precious system to explore the interplay between structural instabilities and superconductivity by tuning the Ca concentration x. We unambiguously detect the softening of phonon modes around the M point on cooling towards the structural transition. Intriguingly, at x = 0:85, the soft mode energy squared at the M point extrapolates to zero at -5.7 K, providing the first compelling microscopic evidence of a structural QCP in (Ca
Sr
)
Rh
Sn
. The enhanced phonon density-of-states at low energy provides the essential ingredient for realizing strong-coupling superconductivity near the structural QCP.
Wu, P.*; Zhang, B.*; Peng, K. L.*; 萩原 雅之*; 石川 喜久*; 古府 麻衣子; Lee, S. H.*; 組頭 広志*; Hu, C. S.*; Qi, Z. M.*; et al.
Physical Review B, 98(9), p.094305_1 - 094305_7, 2018/09
被引用回数:4 パーセンタイル:55.32(Materials Science, Multidisciplinary)熱電材料であるNaドープしたSnSeについて、ARPES, 中性子回折, 中性子非弾性散乱でその電子構造と格子ダイナミクスを測定した結果を報告する。
Xie, T.*; Wei, Y.*; Gong, D.*; Fennell, T.*; Stuhr, U.*; 梶本 亮一; 池内 和彦*; Li, S.*; Hu, J.*; Luo, H.*
Physical Review Letters, 120(26), p.267003_1 - 267003_7, 2018/06
被引用回数:14 パーセンタイル:15.87(Physics, Multidisciplinary)We report an inelastic neutron scattering study on the spin resonance in the bilayer iron-based superconductor CaKFeAs
. In contrast to its quasi-two-dimensional electron structure, three strongly
-dependent modes of spin resonance are found below
= 35 K. The mode energies are below and linearly scale with the total superconducting gaps summed on the nesting hole and electron pockets, essentially in agreement with the results in cuprate and heavy fermion superconductors. This observation supports the sign-reversed Cooper-pairing mechanism under multiple pairing channels and resolves the long-standing puzzles concerning the broadening and dispersive spin resonance peak in iron pnictides. More importantly, the triple resonant modes can be classified into odd and even symmetries with respect to the distance of Fe-Fe planes within the Fe-As bilayer unit. Thus, our results closely resemble those in the bilayer cuprates with nondegenerate spin excitations, suggesting that these two high-
superconducting families share a common nature.
Wang, C.*; Daiwei, Y.*; Liu, X.*; Chen, R.*; Du, X.*; Hu, B.*; Wang, L.*; 飯田 一樹*; 蒲沢 和也*; 脇本 秀一; et al.
Physical Review B, 96(8), p.085111_1 - 085111_5, 2017/08
被引用回数:3 パーセンタイル:71(Materials Science, Multidisciplinary)This paper presents a systematic study of spin and lattice dynamics in the quasi-one-dimensional spiral magnet CuBr, using Raman scattering in conjunction with infrared and neutron spectroscopy. Along with the development of spin correlations upon cooling, we observe a rich set of broad Raman bands at energies that correspond to phonon-dispersion energies near the one-dimensional magnetic wave vector. The low-energy bands further exhibit a distinct intensity maximum at the spiral magnetic ordering temperature.
岩田 隆浩*; 北里 宏平*; 安部 正真*; 大竹 真紀子*; 荒井 武彦*; 荒井 朋子*; 平田 成*; 廣井 孝弘*; 本田 親寿*; 今栄 直也*; et al.
Space Science Reviews, 208(1-4), p.317 - 337, 2017/07
被引用回数:20 パーセンタイル:34.5(Astronomy & Astrophysics)C型小惑星リュウグウを目指す小惑星探査機ハヤブサ2に搭載された近赤外分光計NIRS3は1.8から3.2ミクロンまでの感度を持つ。NIRS3は小惑星の反射スペクトルを計測することで、3ミクロンバンドに現れる水に起因する吸収を検出することを目的としている。InAsフォトダイオードリニアイメージセンサと188Kでの動作を可能とする受動冷却システムによって、本分光計は十分な感度とダークノイズを達成できる。NIRS3フライトモデルは打ち上げ前に地上で性能評価実験が行われ、小惑星表面の水質変成度を決定できるだけのSN比があることが確認された。小惑星表面の計測では、小惑星の熱変性度や、炭素質コンドライトとの対応関係を明らかにできるだろう。
酒井 宏典; Ronning, F.*; 服部 高典; 徳永 陽; 神戸 振作; Zhu, J.-X.*; Wakeham, N.*; 安岡 弘志; Bauer, E. D.*; Thompson, J. D.*
Journal of Physics; Conference Series, 807(3), p.032001_1 - 032001_6, 2017/04
被引用回数:0 パーセンタイル:100量子臨界金属CeCoInのInを少量のCdで置換した時の電子状態を核四重極共鳴(NQR)を用いて調べた。およそ半分のCd置換子周りで局所的にCeの局在モーメントが発生することを、縦緩和率
のサイト依存性から明らかにした。横緩和率
の測定も行い、局在スピン周りでは、
が温度
に比例し、一方、置換子から離れたところでは、
となっており、純CeCoIn
の
に近く、バルクの電子状態は量子臨界状態のままである。
Cheung, Y. W.*; Hu, Y. J.*; Goh, S. K.*; 金子 耕士; 筒井 智嗣; Logg, P. W.*; Grosche, F. M.*; 金川 響*; 谷奥 泰明*; 今井 正樹*; et al.
Journal of Physics; Conference Series, 807(3), p.032002_1 - 032002_4, 2017/04
被引用回数:3 パーセンタイル:14.89(CaSr
)
Rh
Sn
is a member of the substitution series (Ca
Sr
)
Rh
Sn
which has recently been argued to feature a structural quantum critical point at
= 0.9. In the stoichiometric compound Sr
Rh
Sn
, the structural transition at
138 K has been shown to be a second-order phase transition. Moving towards xc, we examine the character of the structural transition in (Ca
Sr
)
Rh
Sn
(i.e.
= 0.5,
55 K) using electrical resistivity, heat capacity and X-ray scattering. The absence of the thermal hysteresis in specific heat around
, and the continuous evolution of the superlattice reflection detected by X-ray diffraction are consistent with the scenario that the structural transition associated with a modulation vector
= (0.5, 0.5, 0) in (Ca
Sr
)
Rh
Sn
remains second-order on approaching the quantum critical point.
Barzakh, A.*; Andreyev, A.; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D. V.*; Fedosseev, V. N.*; Ferrer, R.*; Fink, D. A.*; Ghys, L.*; Huyse, M.*; et al.
Physical Review C, 95(1), p.014324_1 - 014324_12, 2017/01
被引用回数:14 パーセンタイル:11.71(Physics, Nuclear)Hyperfine structure and isotope shifts have been measured for the ground and isomeric states in the neutron deficient isotopes Tl using the 276.9 nm transition. The experiment has been performed at the CERN Isotope Separator On-Line facility using the in-source resonance-ionization laser spectroscopy technique. Spins for the ground states in
Tl have been determined as
= 1/2. Magnetic moments and changes in the nuclear mean-square charge radii have been deduced. By applying the additivity relation for magnetic moments of the odd-odd Tl nuclei the leading configuration assignments were confirmed. A deviation of magnetic moments for isomeric states in
Tl from the trend of the heavier Tl nuclei is observed. The charge radii of the ground states of the isotopes
Tl follow the trend for isotonic (spherical) lead nuclei. The noticeable difference in charge radii for ground and isomeric states of
Tl has been observed, suggesting a larger deformation for the intruder-based 9/2
and 10
states compared to the ground states. An unexpected growth of the isomer shift for
Tl has been found.
Lopez-Martens, A.*; Henning, G.*; Khoo, T. L.*; Seweryniak, D.*; Alcorta, M.*; 浅井 雅人; Back, B. B.*; Bertone, P. F.*; Boilley, D.*; Carpenter, M. P.*; et al.
EPJ Web of Conferences, 131, p.03001_1 - 03001_6, 2016/12
被引用回数:1 パーセンタイル:48.2原子番号が100を超える原子核の核分裂障壁の高さとその角運動量依存性を初めて測定した。核分裂による崩壊が優勢となり始める励起エネルギーを決定できる初期分布法という方法をNoの測定に適用した。
Noの核分裂障壁はスピンゼロにおいて6.6MeVと決定された。このことは、
Noが原子核の殻効果によって強く安定化されていることを示している。
Truesdale, V. L.*; Andreyev, A.; Ghys, L.*; Huyse, M.*; Van Duppen, P.*; Sels, S.*; Andel, B.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; et al.
Physical Review C, 94(3), p.034308_1 - 034308_11, 2016/09
被引用回数:7 パーセンタイル:37.47(Physics, Nuclear)A nuclear-decay spectroscopy study of the neutron-deficient isotope At is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure
decay of
At allowed the low-energy excited states in the daughter nucleus
Bi to be investigated. A
-delayed fission study of
At was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope
Po (populated by
decay of
At) was deduced based on the measured fission-fragment energies. A
DF probability
(
At) = 9(1)
10
was determined.
Hota, S.*; Tandel, S.*; Chowdhury, P.*; Ahmad, I.*; Carpenter, M. P.*; Chiara, C. J.*; Greene, J. P.*; Hoffman, C. R.*; Jackson, E. G.*; Janssens, R. V. F.*; et al.
Physical Review C, 94(2), p.021303_1 - 021303_5, 2016/08
被引用回数:5 パーセンタイル:48.22(Physics, Nuclear)Puにおける
= 8
アイソマーからの崩壊と集団的バンド構造が
Tiと
Pbのビームによる深部非弾性散乱実験によって調べられた。バンド内の正確な
分岐比の測定によって、偶
,
=150アイソトーンにおける
= 8
二準中性子アイソマーが9/2
[734]
7/2
[624]
の配位であることを確かめた。
=152における変形シェルギャップ近傍のこれらのアイソマーは、超重核の一粒子エネルギーの理論的な予言において重要なベンチマークとなる。
Cheung, Y. W.*; Zhang, J. Z.*; Zhu, J. Y.*; Yu, W. C.*; Hu, Y. J.*; Wang, D. G.*; 大友 優香*; 岩佐 和晃*; 金子 耕士; 今井 正樹*; et al.
Physical Review B, 93(24), p.241112_1 - 241112_5, 2016/06
被引用回数:12 パーセンタイル:34.19(Materials Science, Multidisciplinary)The quasi-skutterudite superconductor LaCo
Sn
undergoes a phase transition at
= 152 K. By measuring the temperature dependence of heat capacity, electrical resistivity, and the superlattice reflection intensity using X-ray, we explore the character of the phase transition at
. Our lattice dynamic calculations found imaginary phonon frequencies around the
point, when the high temperature structure is used in the calculations, indicating that the structure is unstable at the zero temperature limit. The combined experimental and computational results establish that
is associated with a second-order structural transition with
= (0.5, 0.5, 0) (or the
point). Further electronic band structure calculations reveal Fermi surface sheets with low-curvature segments, which allow us to draw qualitative comparison with both Sr
Ir
Sn
and Sr
Rh
Sn
in which similar physics has been discussed recently.